Angular velocity sensor

ABSTRACT

An angular velocity sensor for detecting an angular velocity component includes an oscillator having mass, a sensor casing for accommodating the oscillator therewithin, a flexible member for connecting the oscillator to the sensor casing so that the oscillator can be moved with respect to the sensor casing, and capacitance elements including a first electrode provided on a surface of the oscillator and a second electrode provided on a surface of a fixed member fixed to the sensor casing.

This application is a divisional of copending application Ser. No.09/885,620 filed on Jun. 20, 2001 which is a divisional of applicationSer. No. 09/417,338 filed on Oct. 13, 1999 (now U.S. Pat. No.6,282,956), which is a divisional of application Ser. No. 09/067,175filed on Apr. 27, 1998 (now U.S. Pat. No. 5,987,985) which is adivisional of application Ser. No. 08/779,464 filed Jan. 7, 1997 (nowU.S. Pat. No. 5,831,163) which is a divisional of application Ser. No.08/366,026 filed Dec. 29, 1994 (now U.S. Pat. No. 5,646,346) which is aCIP of application Ser. No. 08/331,641 filed on Nov. 10, 1994(abandoned) which is a 371 of PCT/JP93/00390 filed on Mar. 30, 1993claims the benefit thereof and incorporates the same by reference.

TECHNICAL FIELD

This invention relates to an angular velocity sensor, and moreparticularly to a multi-axial angular velocity sensor capable ofindependently detecting angular velocity components about respectiveaxes in an XYZ three-dimensional coordinate system.

BACKGROUND ART

In the automobile industry, machinery industry, and the like, there hasbeen an increased demand for sensors capable of precisely detectingacceleration or angular velocity of a moving object (body). In general,an object which carries out free movement in a three-dimensional spacebears an acceleration in an arbitrary direction and an angular velocityin an arbitrary rotational direction. For this reason, in order toprecisely grasp movement of this object, it is necessary toindependently detect acceleration components in every respectivecoordinate axial direction and angular velocity components about everyrespective coordinate axis in the XYZ three-dimensional coordinatesystem, respectively.

Hitherto, multi-dimensional acceleration sensors of various types havebeen proposed. For example, in the International Laid Open No.WO88/08522 based on the Patent Cooperation Treaty (U.S. Pat. No.4,967,605/ U.S. Pat. No. 5,182,515), there is disclosed an accelerationsensor in which resistance elements formed on a semiconductor substrateare used to detect applied acceleration components in every respectivecoordinate axial direction. Further, in the International Laid Open No.WO91/10118 based on the Patent Cooperation Treaty (U.S. patentapplication Ser. No. 07/761,771), a multi-axial acceleration sensorhaving self-diagnostic function is disclosed. Further, in theInternational Laid Open No. WO92/17759 based on the Patent CooperationTreaty (U.S. patent application Ser. No. 07/952,753), there is disclosedan acceleration sensor in which electrostatic capacitance elements orpiezoelectric elements are used to detect applied accelerationcomponents in every respective coordinate axial direction. Further, alsoin the Japanese Patent Application No. 274299/1990 (Tokuganhei 2-274299)specification and the Japanese Patent Application No. 416188/1990(Tokuganhei 2-416188) specification (U.S. patent application Ser. No.07/764,159), a multi-axial acceleration sensor similar to the above isdisclosed. In the Japanese Patent Application No. 306587/1991(Tokuganhei 3-306587) specification (U.S. patent application Ser. No.07/960,545), a novel electrode arrangement in a similar multi-axialacceleration sensor is disclosed. In addition, in the InternationalApplication PCT/JP92/00882 specification based on the Patent CooperationTreaty, a multi-axial acceleration sensor using piezoelectric element ofanother type is disclosed. The feature of these acceleration sensors isthat a plurality of resistance elements, electrostatic capacitanceelements or piezoelectric elements are arranged at predeterminedpositions of a substrate having flexibility to detect appliedacceleration components on the basis of changes in resistance values ofthe resistance elements, changes in capacitance values of theelectrostatic capacitance elements or changes in voltages produced inthe piezoelectric elements. A weight body is attached on the substratehaving flexibility. When an acceleration is applied, a force is appliedto the weight body and bending occurs in the flexible substrate. Bydetecting this bending on the basis of the above-described changes inresistance values, capacitance values or charges produced, it ispossible to determine acceleration components in respective axialdirections.

On the contrary, the inventor of this application cannot find anyliterature relating to a multi-dimensional angular velocity sensor sofar as he knows. Ordinarily, angular velocity sensors are utilized fordetecting an angular velocity of a power shaft, etc. of a vehicle, andonly have a function to detect an angular velocity about a specificsingle axis. In such cases of determining a rotational velocity of thepower shaft, it is sufficient to use an one-dimensional angular velocitysensor. However, in order to detect angular velocity with respect to anobject which carries out free movement in a three-dimensional space, itis necessary to independently detect angular velocity components aboutrespective axes of the X-axis, the Y-axis and the Z-axis in the XYZthree-dimensional coordinate system. In order to detect angular velocitycomponents about respective axes of the X-axis, the Y-axis and theZ-axis by using one-dimensional angular velocity sensors conventionallyutilized, it is necessary that three sets of angular velocity sensorsare prepared to attach them in specific directions permitting detectionof angular velocity components about respective axes. For this reason,the structure as the entirety of the sensor becomes complicated, and thecost also becomes high.

DISCLOSURE OF THE INVENTION

An object of this invention is to provide a novel multi-axial angularvelocity sensor having a relatively simple structure and capable ofindependently detecting angular velocity components about respectiveaxes of X-axis, Y-axis and Z-axis in XYZ three-dimensional coordinatesystem, respectively.

The fundamental principle utilized in this invention resides in that inthe case where an angular velocity ω about a first coordinate axis isexerted on an oscillator placed in an XYZ three-dimensional coordinatesystem, when this oscillator is oscillated in a second coordinate axisdirection, a Coriolis force proportional to the magnitude of the angularvelocity co is produced in a third coordinate axis direction. In orderto detect angular velocity ω by utilizing this principle, means foroscillating an oscillator in a predetermined coordinate axis direction,and means for detecting displacement in a predetermined coordinate axisdirection produced in the oscillator by action of the Coriolis force arerequired. In addition, in order to detect all of angular velocitycomponent ωx about the X-axis, angular velocity component ωy about theY-axis, and angular velocity component ωz about the Z-axis, means foroscillating the oscillator in three axes directions and means fordetecting displacements in the three axes directions produced in theoscillator are required. This invention provides a sensor having suchmeans, and is characterized as follows.

(1) The first feature of this invention resides in a multi-axial angularvelocity sensor for detecting angular velocity components aboutrespective coordinate axes in a three-dimensional coordinate system,comprising:

an oscillator having mass;

a sensor casing for accommodating this oscillator therewithin;

connection means for connecting the oscillator to the sensor casing inthe state having a degree of freedom such that it can move in respectivecoordinate axes directions;

excitation means for oscillating the oscillator in the respectivecoordinate axes directions; and

displacement detecting means for detecting displacements in therespective coordinate axes directions of the oscillator.

(2) The second feature of this invention resides in that, in theabove-described multi-axial angular velocity sensor having the firstfeature, there is further provided control means for executing:

first detecting operation for giving an indication to the excitationmeans so as to oscillate the oscillator in a first coordinate axisdirection, and for giving an indication to the displacement detectingmeans so as to detect a displacement in a second coordinate axisdirection of the oscillator, thus to determine an angular velocitycomponent about a third coordinate axis on the basis of the detecteddisplacement;

a second detecting operation for giving an indication to the excitationmeans so as to oscillate the oscillator in the second coordinate axisdirection, and for giving an indication to the displacement detectingmeans so as to detect a displacement in a third coordinate axisdirection of the oscillator, thus to determine an angular velocitycomponent about a first coordinate axis on the basis of the detecteddisplacement; and

a third detecting operation for giving an indication to the excitationmeans so as to oscillate the oscillator in the third coordinate axisdirection, and for giving an indication to the displacement detectingmeans so as to detect a displacement in the first coordinate axisdirection of the oscillator, thus to determine an angular velocitycomponent about the second coordinate axis on the basis of the detecteddisplacement.

(3) The third feature of this invention resides in that, in theabove-described multi-axial angular velocity sensor having the secondfeature, the control means is caused to further execute a fourthdetecting operation for giving an indication to the excitation means soas not to oscillate the oscillator in any direction, and for giving anindication to the displacement detecting means so as to detectdisplacements in all the first to third coordinate axial directions ofthe oscillator, thus to determine acceleration components exerted inrespective coordinate axial directions on the basis of the detecteddisplacements.

(4) The fourth feature of this invention resides in that, in amulti-axial angular velocity sensor for detecting angular velocitycomponents about respective coordinate axes in a three-dimensionalcoordinate system, there are provided:

a flexible substrate having flexibility;

a fixed substrate disposed so as to oppose the flexible substrate with apredetermined distance therebetween above the flexible substrate;

an oscillator fixed on the lower surface of the flexible substrate;

a sensor casing for supporting the flexible substrate and the fixedsubstrate and accommodating the oscillator therewithin;

excitation means for oscillating the oscillator in respective coordinateaxial directions; and

displacement detecting means for detecting displacements in respectivecoordinate axial directions of the oscillator.

(5) The fifth feature of this invention resides in that, in amulti-axial angular velocity sensor for detecting angular velocitycomponents about respective coordinate axes in a three-dimensionalcoordinate system, there are provided:

a flexible substrate having flexibility;

a fixed substrate disposed so as to oppose the flexible substrate with apredetermined distance therebetween above the flexible substrate;

an oscillator fixed on the lower surface of the flexible substrate;

a sensor casing for supporting the flexible substrate and the fixedsubstrate and accommodating the oscillator therewithin;

a plurality of lower electrodes formed on the upper surface of theflexible substrate;

a plurality of upper electrodes formed on the lower surface of the fixedsubstrate and disposed at positions respectively opposite to theplurality of lower electrodes;

means for applying an a.c. signal across a predetermined pair of lowerand upper electrodes opposite to each other to thereby oscillate theoscillator in respective coordinate axial directions; and

means for determining an electrostatic capacitance between thepredetermined pair of lower and upper electrodes opposite to each otherto thereby detect displacements in respective coordinate axialdirections of the oscillator.

(6) The sixth feature of this invention resides in that, in theabove-described multi-axial angular velocity sensor having the fifthfeature,

an XYZ three-dimensional coordinate system such that an X-axis and aY-axis intersect with each other on a plane in parallel to the principalsurface of the flexible substrate is defined; and

a first lower electrode and a first upper electrode are disposed in thepositive region of the X-axis, a second lower electrode and a secondupper electrode are disposed in the negative region of the X-axis, athird lower electrode and a third upper electrode are disposed in thepositive region of the Y-axis, a fourth lower electrode and a fourthupper electrode are disposed in the negative region of the Y-axis, and afifth lower electrode and a fifth upper electrode are arranged at aposition corresponding to the origin.

(7) The seventh feature of this invention resides in that, in theabove-described multi-axial angular velocity sensor having the sixthfeature, there is further provided control means for executing:

a first detecting operation for applying an a.c. signal across the fifthlower electrode and the fifth upper electrode to determine, with theoscillator being oscillated in a Z-axis direction, a difference betweenan electrostatic capacitance between the third lower electrode and thethird upper electrode and an electrostatic capacitance between thefourth lower electrode and the fourth upper electrode, thus to detect anangular velocity component about the X-axis on the basis of thisdifference;

a second detecting operation for applying a.c. signals having phasesopposite to each other across the first lower electrode and the firstupper electrode and across the second lower electrode and the secondupper electrode to determine, with the oscillator being oscillated inthe X-axis direction, an electrostatic capacitance between the fifthlower electrode and the fifth upper electrode, thus to detect an angularvelocity component about the Y-axis on the basis of this electrostaticcapacitance; and

a third detecting operation for applying a.c. signals having phasesopposite to each other across the third lower electrode and the thirdupper electrode and across the fourth lower electrode and the fourthupper electrode to determine, with the oscillator being oscillated inthe Y-axis direction, a difference between an electrostatic capacitancebetween the first lower electrode and the first upper electrode and anelectrostatic capacitance between the second lower electrode and thesecond upper electrode, thus to detect an angular velocity componentabout the Z-axis on the basis of the difference.

(8) The eighth feature of this invention resides in that, in theabove-described multi-axial angular velocity sensors having the fifth toseventh features, arrangement of electrodes is changed. Namely, theeight feature resides in that:

an XYZ three-dimensional coordinate system such that the X-axis and theY-axis intersect with each other on a plane in parallel to the principalsurface of the flexible substrate is defined; and

the first lower electrode and the first upper electrode are disposed inthe first quadrant region with respect to the XY plane, the second lowerelectrode and the second upper electrode are disposed in the secondquadrant region with respect to the XY plane, the third lower electrodeand the third upper electrode are disposed in the third quadrant regionwith respect to the XY plane, the fourth lower electrode and the fourthupper electrode are disposed in the fourth quadrant region with respectto the XY plane, and the fifth lower electrode and the fifth upperelectrode are disposed at a position corresponding to the origin.

(9) The ninth feature of this invention resides in that, in theabove-described multi-axial angular velocity sensors having the fifth tothe eight features, piezo-resistance elements are disposed on theflexible substrate, and means for detecting changes in resistance valuesof these piezo-resistance elements is provided in place of means fordetecting electrostatic capacitance, thus to detect displacements inrespective coordinate axial directions of the oscillator by changes ofthe resistance values.

(10) The tenth feature of this invention resides in that, in theabove-described multi-axial angular velocity sensors having the fifth tothe eight features, piezoelectric elements are interposed betweenrespective upper electrodes and respective lower electrodes to deliveran a.c. signal to these piezoelectric elements to thereby oscillate theoscillator in respective coordinate axial directions, and to detectvoltages produced by these piezoelectric elements to thereby detectdisplacements in respective coordinate axial directions of theoscillator.

(11) The eleventh feature of this invention resides in that, in amulti-axial angular velocity sensor for detecting angular velocitycomponents about respective coordinate axes in a three-dimensionalcoordinate system, there are provided:

a piezoelectric element in a plate form;

a plurality of upper electrodes formed on the upper surface of thepiezoelectric element;

a plurality of lower electrodes formed on the lower surface of thepiezoelectric element and disposed at positions respectively opposite tothe plurality of upper electrodes;

a flexible substrate fixed on the lower surface of the lower electrodeand having flexibility;

an oscillator fixed on the lower surface of the flexible substrate;

a sensor casing for supporting the flexible substrate and accommodatingthe oscillator therewithin;

means for applying an a.c. signal across a predetermined pair of lowerand upper electrodes opposite to each other to thereby oscillate theoscillator in respective coordinate axial directions; and

means for measuring a voltage produced across the predetermined pair oflower and upper electrodes opposite to each other to thereby detectdisplacements in respective coordinate axial directions of theoscillator.

(12) The twelfth feature of this invention resides in that, in theabove-described multi-axial angular velocity sensor utilizingpiezoelectric element, the polarization characteristic of thepiezoelectric element is partially inverted.

(13) The thirteenth feature of this invention resides in that, in theabove-described multi-axial angular velocity sensor utilizingpiezoelectric element, a plurality of piezoelectric elements physicallydivided are used.

(14) The fourteenth feature of this invention resides in that, in theabove-described respective multi-axial angular velocity sensors, eitherone group of the plural lower electrodes or the plural upper electrodesis constituted with a single electrode layer.

(15) The fifteenth feature of this invention resides in that, in theabove-described multi-axial angular velocity sensor having thefourteenth feature, the flexible substrate or the fixed substrate isconstituted with a conductive material, and the conductive substrateitself is used as a single electrode layer.

(16) The sixteenth feature of this invention resides in that, in amulti-axial angular velocity sensor for detecting angular velocitycomponents about respective coordinate axes in a three-dimensionalcoordinate system, there are provided:

an oscillator comprised of a magnetic material, which is disposed at theorigin position of the coordinate system;

a sensor casing for accommodating the oscillator therewithin;

connection means for connecting the oscillator to the sensor casing inthe state having a degree of freedom such that it can move in respectivecoordinate axial directions;

a first coil pair attached to the sensor casing at positive and negativepositions of a first coordinate axis of the coordinate system;

a second coil pair attached to the sensor casing at positive andnegative positions of a second coordinate axis of the coordinate system;

a third coil pair attached to the sensor casing at positive and negativepositions of a third coordinate axis of the coordinate system;

excitation means for delivering a predetermined an a.c. signal to therespective coil pairs to thereby oscillate the oscillator in respectivecoordinate axes directions; and

displacement detecting means for detecting displacements in respectivecoordinate axes directions of the oscillator on the basis of changes inimpedance of respective coil pairs.

(17) The seventeenth feature of this invention resides in that, in theabove-described multi-axial angular velocity sensor having the sixteenthfeature, there is further provided control means for executing:

a first detecting operation for delivering an a.c. signal to the firstcoil pair to determine a change of impedance of the second coil pairwith the oscillator being oscillated in the first axial direction todetect an angular velocity component about the third axis on the basisof the change of impedance;

a second detecting operation for delivering an a.c. signal to the secondcoil pair to determine a change of impedance of the third coil pair withthe oscillator being oscillated in the second axial direction to detectan angular velocity component about the first axis on the basis of thechange of impedance; and

a third detecting operation for delivering an a.c. signal to the thirdcoil pair to determine a change of impedance of the first coil pair withthe oscillator being oscillated in the third axial direction to detectan angular velocity component about the second axis on the basis of thechange of impedance.

(18) The eighteenth feature of this invention resides in that, in amulti-axial angular velocity sensor for detecting angular velocitycomponents about at least two coordinate axes in a three-dimensionalcoordinate system, there are provided:

an oscillator having mass;

a sensor casing for accommodating the oscillator therewithin;

connection means for connecting the oscillator to the sensor casing inthe state having a degree of freedom such that it can move in respectivethree coordinate axial directions;

excitation means for oscillating the oscillator in at least twocoordinate axial directions; and

displacement detecting means for detecting displacements in at least twocoordinate axial directions of the oscillator.

(19) The nineteenth feature of this invention resides in that, in theabove-described multi-axial angular velocity sensor having theeighteenth feature, there is provided control means for executing:

a first detecting operation for giving an indication to the excitationmeans so as to oscillate the oscillator in the first coordinate axisdirection, and for giving an indication to the displacement detectingmeans so as to detect a displacement in the second coordinate axisdirection of the oscillator, thus to determine an angular velocitycomponent about the third coordinate axis on the basis of the detecteddisplacement; and

a second detecting operation for giving an indication to the excitationmeans so as to oscillate the oscillator in the second coordinate axisdirection, and for giving an indication to the displacement detectingmeans so as to detect a displacement in the third coordinate axisdirection of the oscillator, thus to determine an angular velocitycomponent about the first coordinate axis on the basis of the detecteddisplacement.

(20) The twentieth feature of this invention resides in that, in amulti-axial angular velocity sensor for detecting angular velocitycomponents about two coordinate axes in a three-dimensional coordinatesystem, there are provided:

an oscillator having mass;

a sensor casing for accommodating the oscillator therewithin;

connection means for connecting the oscillator to the sensor casing inthe state having a degree of freedom such that it can move in respectivethree coordinate axial directions;

excitation means for oscillating the oscillator in the first coordinateaxis direction; and

displacement detecting means for detecting displacements in the secondcoordinate axis direction and in the third coordinate axis direction ofthe oscillator,

to determine an angular velocity component about the third coordinateaxis on the basis of the displacement in the second coordinate axisdirection detected by the displacement detecting means, and

to determine an angular velocity component about the second coordinateaxis on the basis of the displacement in the third coordinate axisdirection detected by the displacement detecting means.

(21) The twenty first feature of this invention resides in that, in amulti-axial angular velocity sensor for detecting angular velocitycomponents about two coordinate axes in a three-dimensional coordinatesystem, there are provided:

an oscillator having mass;

a sensor casing for accommodating the oscillator therewithin;

connection means for connecting the oscillator to the sensor casing inthe state having a degree of freedom such that it can move in threecoordinate axial directions;

excitation means for oscillating the oscillator in the first coordinateaxis direction and in the second coordinate axis direction; and

displacement detecting means for detecting a displacement in the thirdcoordinate axis direction of the oscillator,

to determine an angular velocity component about the second coordinateaxis on the basis of the displacement in the third coordinate axisdirection detected by the displacement detecting means when theoscillator is oscillating in the first coordinate axis direction, and

to determine an angular velocity component about the first coordinateaxis on the basis of the displacement in the third coordinate axisdirection detected by the displacement detecting means when theoscillator is oscillating in the second coordinate axis direction.

(22) The twenty second feature of this invention resides in that, in amulti-axial angular velocity sensor for detecting angular velocitycomponents about respective coordinate axes in a three-dimensionalcoordinate system, there are provided:

an oscillator having mass;

a sensor casing for accommodating the oscillator therewithin;

connection means for connecting the oscillator to the sensor casing inthe state having a degree of freedom such that it can move in respectivethree coordinate axes directions;

excitation means for oscillating the oscillator in the first coordinateaxis direction and in the second coordinate direction; and

displacement detecting means for detecting a displacement in the secondcoordinate axis direction and a displacement in the third coordinateaxis direction of the oscillator,

to determine an angular velocity component about the third coordinateaxis on the basis of the displacement in the second coordinate axisdirection detected by the displacement detecting means when theoscillator is oscillating in the first coordinate axis direction,

to determine an angular velocity component about the second coordinateaxis on the basis of the displacement in the third coordinate axisdirection detected by the displacement detecting means when theoscillator is oscillating in the first coordinate axis direction, and

to determine an angular velocity component about the first coordinateaxis on the basis of the displacement in the third coordinate axisdirection detected by the displacement detecting means when theoscillator is oscillating in the second coordinate axis direction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing the fundamental principle of anone-dimensional angular velocity sensor utilizing Coriolis forceconventionally proposed.

FIG. 2 is a view showing angular velocity components about respectiveaxes in an XYZ three-dimensional coordinate system, which are to bedetected in this invention.

FIG. 3 is a view for explaining the fundamental principle for detectingan angular velocity component ωx about the X-axis by this invention.

FIG. 4 is a view for explaining the fundamental principle for detectingan angular velocity component ωy about the Y-axis by this invention.

FIG. 5 is a view for explaining the fundamental principle for detectingan angular velocity component ωz about the Z-axis by this invention.

FIG. 6 is a side cross sectional view showing the structure of amulti-axial angular velocity sensor according to a first embodiment ofthis invention.

FIG. 7 is a top view of flexible substrate 110 of the multi-axialangular velocity sensor shown in FIG. 6.

FIG. 8 is a bottom view of fixed substrate 120 of the multi-axialangular velocity sensor shown in FIG. 6.

FIG. 9 is a side cross sectional view showing the IS state whereoscillator 130 in the multi-axial angular velocity sensor shown in FIG.6 is caused to undergo displacement in the X-axis direction.

FIG. 10 is a side cross sectional view showing the state whereoscillator 130 in the multi-axial angular velocity sensor shown in FIG.6 is caused to undergo displacement in the −X axis direction.

FIG. 11 is a side cross sectional view showing the state whereoscillator 130 in the multi-axial velocity sensor shown in FIG. 6 iscaused to undergo displacement in the Z-axis direction.

FIG. 12 is a view showing a voltage waveform supplied for allowingoscillator 130 to produce oscillation Ux in the X-axis direction in themulti-axial angular velocity sensor shown in FIG. 6.

FIG. 13 is a view showing a voltage waveform supplied for allowingoscillator 130 to produce oscillation Uy in the Y-axis direction in themulti-axial angular velocity sensor shown in FIG. 6.

FIG. 14 is a view showing a voltage waveform supplied for allowingoscillator 130 to produce oscillation Uz in the Z-axis direction in themulti-axial angular velocity sensor shown in FIG. 6.

FIG. 15 is a side cross sectional view showing the phenomenon thatCoriolis force Fy is produced on the basis of angular velocity componentωx when oscillator 130 is caused to produce oscillation Uz in themulti-axial angular velocity sensor shown in FIG. 6.

FIG. 16 is a side cross sectional view showing the phenomenon thatCoriolis force Fz is produced on the basis of angular velocity componentωy when oscillator 130 is caused to produce oscillation Ux in themulti-axial angular velocity sensor shown in FIG. 6.

FIG. 17 is a side cross sectional view showing the phenomenon thatCoriolis force Fx is produced on the basis of angular velocity componentωz when oscillator 130 is caused to produce oscillation Uy in themulti-axial angular velocity sensor shown in FIG. 6.

FIG. 18 is a circuit diagram showing an example of a circuit fordetecting change of a capacitance value of electrostatic capacitanceelement C.

FIG. 19 is a timing chart for explaining the operation of the circuitshown in FIG. 18.

FIG. 20 is a circuit diagram showing an example of a circuit fordetecting changes of capacitance values of a pair of electrostaticcapacitance elements C1, C2.

FIG. 21 is a timing chart for explaining the operation of the circuitshown in FIG. 20.

FIG. 22 is a side cross sectional view for explaining the principle of afirst modification of the multi-axial angular velocity sensor shown inFIG. 6.

FIG. 23 is another side cross sectional view for explaining theprinciple of the first modification of the multi-axial angular velocitysensor shown in FIG. 6.

FIG. 24 is a further side cross sectional view for explaining theprinciple of the first modification of the multi-axial angular velocitysensor shown in FIG. 6.

FIG. 25 is a side cross sectional view showing a more practicalstructure of the first modification of the multi-axial angular velocitysensor shown in FIG. 6.

FIG. 26 is a view showing an example of a method of applying a voltageto respective electrodes of the multi-axial angular velocity sensorshown in FIG. 25.

FIG. 27 is a side cross sectional view showing a more practicalstructure of a second modification of the multi-axial angular velocitysensor shown in FIG. 6.

FIG. 28 is a side cross sectional view showing the structure of amulti-axial angular velocity sensor according to a second embodiment ofthis invention.

FIG. 29 is a top view of flexible substrate 210 of the multi-axialangular velocity sensor shown in FIG. 28.

FIG. 30 is a side cross sectional view showing a cross section atanother position of the multi-axial angular velocity sensor shown inFIG. 28.

FIG. 31 is a bottom view of fixed substrate 230 of the multi-axialangular velocity sensor shown in FIG. 28.

FIG. 32 is a side cross sectional view showing a first modification ofthe multi-axial angular velocity sensor shown in FIG. 28.

FIG. 33 is a side cross sectional view showing a second modification ofthe multi-axial angular velocity sensor shown in FIG. 28.

FIG. 34 is a top view of flexible substrate 250 of the multi-axialangular velocity sensor shown in FIG. 33.

FIG. 35 is a side cross sectional view showing the structure of amulti-axial angular velocity sensor according to a third embodiment ofthis invention.

FIG. 36 is a top view of flexible substrate 310 of the multi-axialangular velocity sensor shown in FIG. 35.

FIG. 37 is a view showing arrangement of resistance elements R shown inFIG. 36.

FIG. 38 is a side cross sectional view showing a state where Coriolisforce Fx is exerted on the multi-axial angular velocity sensor shown inFIG. 35.

FIG. 39 is a circuit diagram showing an example of a circuit fordetecting Coriolis force Fx in the X-axis direction exerted on themulti-axial angular velocity sensor shown in FIG. 35.

FIG. 40 is a circuit diagram showing an example of a circuit fordetecting Coriolis force Fy in the Y-axis direction exerted on themulti-axial angular velocity sensor shown in FIG. 35.

FIG. 41 is a circuit diagram showing an example of a circuit fordetecting Coriolis force Fz in the Z-axis direction exerted on themulti-axial angular velocity sensor shown in FIG. 35.

FIG. 42 is a side cross sectional view showing a structure of amulti-axial angular velocity sensor according to a fourth embodiment ofthis invention.

FIGS. 43(a) and 43(b) are views showing a polarization characteristic ofa piezoelectric element used in the multi-axial angular velocity sensorshown in FIG. 42.

FIG. 44 is a side cross sectional view showing a state where themulti-axial angular velocity sensor shown in FIG. 42 is caused toundergo displacement in the X-axis direction.

FIG. 45 is a side cross sectional view showing a state where themulti-axial angular velocity sensor shown in FIG. 42 is caused toundergo displacement in the Z-axis direction.

FIG. 46 is a wiring diagram showing a wiring for detecting Coriolisforce Fx in the X-axis direction exerted on the multi-axial angularvelocity sensor shown in FIG. 42.

FIG. 47 is a wiring diagram showing a wiring for detecting Coriolisforce Fy in the Y-axis direction exerted on the multi-axial angularvelocity sensor shown in FIG. 42.

FIG. 48 is a wiring diagram showing a wiring for detecting Coriolisforce Fz in the Z-axis direction exerted on the multi-axial angularvelocity sensor shown in FIG. 42.

FIGS. 49(a) and 49(b) are views showing a polarization characteristicopposite to the polarization characteristic shown in FIGS. 43(a) and43(b).

FIG. 50 is a plan view showing a distribution of the polarizationcharacteristics of a piezoelectric element used in the firstmodification of the multi-axial angular velocity sensor shown in FIG.42.

FIG. 51 is a wiring diagram showing a wiring for detecting Coriolisforce Fx in the X-axis direction exerted on the multi-axial angularvelocity sensor using piezoelectric elements shown in FIG. 50.

FIG. 52 is a wiring diagram showing a wiring for detecting Coriolisforce Fy in the Y-axis direction exerted on the multi-axial angularvelocity sensor using piezoelectric elements shown in FIG. 50.

FIG. 53 is a wiring diagram showing a wiring for detecting Coriolisforce Fz in the Z-axis direction exerted on the multi-axial angularvelocity sensor using piezoelectric elements shown in FIG. 50.

FIG. 54 is a side cross sectional view showing a structure of a secondmodification of the multi-axial angular velocity sensor shown in FIG.42.

FIG. 55 is a side cross sectional view showing a structure of a thirdmodification of the multi-axial angular velocity sensor shown in FIG.42.

FIG. 56 is a side cross sectional view showing a structure of a fourthmodification of the multi-axial angular velocity sensor shown in FIG.42.

FIG. 57 is a top view showing a structure of a multi-axial angularvelocity sensor according to a fifth embodiment of this invention.

FIG. 58 is a side cross sectional view showing the structure of themulti-axial angular velocity sensor shown in FIG. 57.

FIG. 59 is a top view showing an arrangement of localized elementsdefined in the multi-axial angular velocity sensor shown in FIG. 57.

FIGS. 60(a) and 60(b) are views showing a polarization characteristic ofa piezoelectric element used in the multi-axial angular velocity sensorshown in FIG. 57.

FIG. 61 is a side cross sectional view showing a state where themulti-axial angular velocity sensor shown in FIG. 57 is caused toundergo displacement in the X-axis direction.

FIG. 62 is a side cross sectional view showing a state where themulti-axial angular velocity sensor shown in FIG. 57 is caused toundergo displacement in the Z-axis direction.

FIG. 63 is a wiring diagram showing a wiring for detecting Coriolisforce Fx in the X-axis direction exerted on the multi-axial angularvelocity sensor shown in FIG. 57.

FIG. 64 is a wiring diagram showing a wiring for detecting Coriolisforce Fy in the Y-axis direction exerted on the multi-axial angularvelocity sensor shown in FIG. 57.

FIG. 65 is a wiring diagram showing a wiring for detecting Coriolisforce Fz in the Z-axis direction exerted on the multi-axial angularvelocity sensor shown in FIG. 57.

FIGS. 66(a) and 66(b) are views showing a polarization characteristicopposite to the polarization characteristic shown in FIG. 60.

FIG. 67 is a plan view showing a distribution of the polarizationcharacteristics of a piezoelectric element used in the firstmodification of the multi-axial angular velocity sensor shown in FIG.57.

FIG. 68 is a side cross sectional view showing a state where Coriolisforce Fx in the X-axis direction is exerted on the multi-axial angularvelocity sensor using the piezoelectric element shown in FIG. 67.

FIG. 69 is a side cross sectional view showing a state where Coriolisforce Fz in the Z-axis direction is exerted on the multi-axial angularvelocity sensor using the piezoelectric element shown in FIG. 67.

FIG. 70 is a wiring diagram showing a wiring for detecting Coriolisforce Fx in the X-axis direction exerted on the multi-axial angularvelocity sensor using the piezoelectric element shown in FIG. 67.

FIG. 71 is a wiring diagram showing a wiring for detecting Coriolisforce Fy in the Y-axis direction exerted on the multi-axial angularvelocity sensor using the piezoelectric element shown in FIG. 67.

FIG. 72 is a wiring diagram showing a wiring for detecting Coriolisforce Fz in the Z-axis direction exerted on the multi-axial angularvelocity sensor using the piezoelectric element shown in FIG. 67.

FIG. 73 is a side cross sectional view showing a structure of a secondmodification of the multi-axial angular velocity sensor shown in FIG.57.

FIG. 74 is a side cross sectional view showing a structure of a thirdmodification of the multi-axial angular velocity sensor shown in FIG.57.

FIG. 75 is a perspective view showing a fundamental principle of amulti-axial angular velocity sensor according to a sixth embodiment ofthis invention.

FIG. 76 is a side cross sectional view showing a more practicalstructure of the multi-axial angular velocity sensor according to thesixth embodiment of this invention.

FIG. 77 is a flowchart showing a procedure of a detecting operation inthe multi-axial angular velocity sensor according to this invention.

FIG. 78 is a view showing an actual example of a circuit configurationfor carrying out the detecting operation in the multi-axial angularvelocity sensor according to this invention.

FIG. 79 is a view for explaining another fundamental principle fordetecting angular velocity component ωx about the X-axis by thisinvention.

FIG. 80 is a view for explaining a further fundamental principle fordetecting angular velocity component ωy about the Y-axis by thisinvention.

FIG. 81 is a view for explaining a still further fundamental principlefor detecting angular velocity component ωz about the Z-axis by thisinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

§0 Fundamental Principle

<0.1> Uni-axial Angular Velocity Sensor

Initially, the detection principle of angular velocity by a uni-axialangular velocity sensor which forms the foundation of a multi-axialangular velocity sensor according to this invention will be brieflydescribed. FIG. 1 is a view showing the fundamental principle of anangular velocity sensor disclosed in Magazine “THE INVENTION” compliedunder the supervision of the Japanese Patent Office, vol. 90, No. 3(1993), page 60. An oscillator 10 in a square pillar is prepared andconsideration is now made in connection with an XYZ three-dimensionalcoordinate system in which X-, Y- and Z-axes are defined in directionsas shown. In such a system, in the case where oscillator 10 is carryingout rotational movement at an angular velocity ω with the Z-axis beingas the axis of rotation, it is known that a phenomenon as describedbelow takes place. Namely, when the oscillator 10 is caused to producesuch an oscillation U to reciprocate it in the X-axis direction, aCoriolis force F takes place in the Y-axis direction. In other words,when oscillator 10 is rotated with the Z-axis being as a center axis inthe state where it is oscillated along the X-axis of the figure,Coriolis force F is to be produced in the Y-axis direction. Thisphenomenon is the dynamical phenomenon known for long as Foucault'spendulum. A Coriolis force F produced is expressed as follows:F=2m·v·ω

In the above expression, m is a mass of oscillator 10, v is aninstantaneous velocity with respect to oscillation of the oscillator 10,and ω is an instantaneous angular velocity of the oscillator 10.

The uni-axial angular velocity sensor disclosed in the previouslydescribed magazine serves to detect an angular velocity ω by making useof the above phenomenon. Namely, as shown in FIG. 1, a firstpiezoelectric element 11 is attached on a first surface of theoscillator 10 in a square pillar form, and a second piezoelectricelement 12 is attached on a second surface perpendicular to the firstsurface. As the piezoelectric elements 11, 12, an element in a plateform comprised of piezoelectric ceramic is used. In order to allow theoscillator 10 to produce oscillation U, the piezoelectric element 11 isutilized. Further, in order to detect a Coriolis force F produced, thepiezoelectric element 12 is utilized. Namely, when an a.c. voltage isapplied to the piezoelectric element 11, this piezoelectric element 11repeats expansive and contractive movements and oscillates in the X-axisdirection. This oscillation U is transmitted to the oscillator 10, sothe oscillator 10 oscillates in the X-axis direction. As stated above,when the oscillator 10 itself rotates at an angular velocity ω with theZ-axis being as a center axis in the state where the oscillator 10 iscaused to undergo oscillation U, a Coriolis force F is produced in theY-axis direction by the above-described phenomenon. Since this Coriolisforce F is exerted in a thickness direction of the piezoelectric element12, a voltage V proportional to the Coriolis force F is produced acrossboth the surfaces of the piezoelectric element 12. Accordingly, bymeasuring this voltage V, it becomes possible to detect angular velocityω.

<0.2> Multi-axial Angular Velocity Sensor

The above-described conventional angular velocity sensor serves todetect an angular velocity component about the Z-axis, and this sensoris therefore unable to detect an angular velocity component about theX-axis or the Y-axis. This invention contemplates providing, as shown inFIG. 2, a multi-axial angular velocity sensor capable of independentlydetecting an angular velocity component ωx about the X-axis, an angularvelocity component ωy about the Y-axis, and an angular velocitycomponent ωz about the Z-axis in the XYZ three-dimensional coordinatesystem with respect to a predetermined object 20. The fundamentalprinciple thereof will now be described with reference to FIGS. 3 to 5.It is now assumed that an oscillator 30 is placed at the origin positionof XYZ three-dimensional coordinate system. In order to detect angularvelocity component ωx about the X-axis of the oscillator 30, it issufficient to measure a Coriolis force Fy produced in the Y-axisdirection when the oscillator 30 is caused to undergo oscillation Uz inthe Z-axis direction as shown in FIG. 3. The Coriolis force Fy takes avalue proportional to angular velocity component ωx. Further, in orderto detect angular velocity ωy about the Y-axis of the oscillator 30, itis sufficient to measure a Coriolis force Fz produced in the Z-axisdirection when the oscillator 30 is caused to undergo oscillation Ux inthe X-axis direction as shown in FIG. 4. The Coriolis force Fz takes avalue proportional to angular velocity ωy. In addition, in order todetect angular velocity component ωz about the Z-axis of the oscillator30, it is sufficient to measure a Coriolis force Fx produced in theX-axis direction when the oscillator 30 is caused to undergo oscillationUy in the Y-axis direction. The Coriolis force Fx takes a valueproportional to angular velocity ωz.

Eventually, in order to detect angular velocity components everyrespective axes in the XYZ three-dimensional coordinate system, themechanism for oscillating the oscillator 30 in the X-axis direction, themechanism for oscillating it in the Y-axis direction, and the mechanismfor oscillating it in the Z-axis direction; and the mechanism fordetecting Coriolis force Fx in the X-axis direction exerted on theoscillator 30, the mechanism for detecting Coriolis force Fy in theY-axis exerted thereon, and the mechanism for detecting Coriolis forceFz in the Z-axis exerted thereon are required.

<0.3> Oscillation Mechanism/Detection Mechanism

As described above, in the multi-axial angular velocity sensor accordingto this invention, the mechanism for oscillating the oscillator in aspecific coordinate axis direction, and the mechanism for detecting aCoriolis force in a specific coordinate axis direction exerted on theoscillator are required. As the oscillation mechanism, respectivemechanism as described below may be utilized.

(1) Mechanism Utilizing Coulomb Force:

A first electrode and a second electrode are respectively formed on theoscillator side and on the sensor casing side to dispose a pair ofelectrodes in a manner opposite to each other. If charges of the samepolarity are delivered to the both electrodes, a repulsive force isexerted. In contrast, if charges of different polarities are delivered,an attractive force is exerted. Accordingly, when an approach isemployed to allow the both electrodes to interchangeably undergorepulsive force and attractive force exerted therebetween, theoscillator oscillates relative to the sensor casing.

(2) Mechanism Utilizing Piezoelectric Element:

This mechanism is the mechanism used in the uni-axial angular velocitysensor shown in FIG. 1. By applying an a.c. voltage across thepiezoelectric element 11, the oscillator 10 is oscillated.

(3) Mechanism Utilizing Electromagnetic Force:

An oscillator comprised of a magnetic material is used and a coil isdisposed on the sensor casing side to allow a current to flow in thecoil to exert an electromagnetic force thereon to oscillate theoscillator.

On the other hand, as the mechanism for detecting Coriolis force,respective mechanism as described below may be utilized.

(1) Mechanism Utilizing Change of the Electrostatic Capacitance:

A first electrode and a second electrode are respectively formed on theoscillator side and on the sensor casing side to dispose a pair ofelectrodes in a manner opposite to each other. When a Coriolis force isapplied to the oscillator, so displacement takes place, the spacing(distance) between the both electrodes varies. For this reason, theelectrostatic capacitance value of an electrostatic capacitance elementconstituted by the both electrodes varies. By measuring a change of thecapacitance value, the applied Coriolis force is detected.

(2) Mechanism Utilizing Piezoelectric Element:

This mechanism is the mechanism used in the uni-axial angular velocitysensor shown in FIG. 1. When a Coriolis force F is applied to thepiezoelectric element 12, the piezoelectric element 12 produces avoltage proportional to the Coriolis force F. By measuring the voltagethus produced, the applied Coriolis force is detected.

(3) Mechanism Utilizing Differential Transformer:

An oscillator comprised of a magnetic material is used and a coil isdisposed on the sensor casing side. When a Coriolis force is applied tothe oscillator, so any displacement takes place, the distance betweenthe oscillator and the coil varies. For this reason, inductance of thecoil varies. By measuring a change of the inductance, the appliedCoriolis force is detected.

(4) Mechanism Utilizing Piezo-Resistance Element:

A substrate such that bending takes place when a Coriolis force isapplied thereto is provided. A piezo-resistance element is formed on thesubstrate to detect a bending produced in the substrate as a change ofthe resistance value of the piezo-resistance element. Namely, bymeasuring a change of the resistance value, the applied Coriolis forceis detected.

While the fundamental principle of the multi-axial angular velocitysensor according to this invention has been briefly described, morepractical examples of sensors of a simple structure operative on thebasis of such fundamental principle will now be described below.

§1 First Embodiment

<1.1> Structure of Sensor According to First Embodiment

A multi-axial angular velocity sensor according to the first embodimentof this invention will be first described. The sensor of the firstembodiment is a sensor in which a mechanism utilizing Coulomb force isused as the oscillation mechanism and a mechanism utilizing change ofelectrostatic capacitance is used as the detection mechanism.

FIG. 6 is a side cross sectional view of the multi-axial angularvelocity sensor according to the first embodiment. A flexible substrate110 and a fixed substrate 120 are both a disk-shaped substrate, and aredisposed in parallel to each other with a predetermined spacing(distance) therebetween. On the lower surface of the flexible substrate110, a columnar oscillator 130 is fixed. Further, the outercircumferential portion of the flexible substrate 110 and the outercircumferential portion of the fixed substrate 120 are both supported bya sensor casing 140. On the lower surface of the fixed substrate 120,five upper electrode layers E1 to E5 (only a portion thereof isindicated in FIG. 6) are formed. Similarly, on the upper surface of theflexible substrate 110, five lower electrode layers F1 to F5 (only aportion thereof is also indicated) are formed. In this embodiment, thefixed substrate 120 has sufficient rigidity, so there is no possibilitythat bending may take place. On the other hand, since the flexiblesubstrate 110 has flexibility, it functions as so called a diaphragm.The oscillator 130 is constituted with a material having a weightsufficient to produce a stable oscillation. For convenience ofexplanation, consideration will be made in connection with an XYZthree-dimensional coordinate system in which the gravity position O ofoscillator 130 is assumed as the origin. Namely, X-axis is defined in aright direction of the figure, Z-axis is defined in an upper directionthereof, and Y-axis is defined in a direction perpendicular to planesurface of paper. It can be said that FIG. 6 is a cross sectional viewcut along the XZ plane of the sensor. It is to be noted that, in thisembodiment, the flexible substrate 110 and the fixed substrate 120 areboth constituted by an insulating material. In the case where there is anecessity of constituting these substrates with a conductive materialsuch as metal, etc., it is sufficient to form respective electrodelayers through insulating films so that these electrode layers are notshort-circuited.

The shape and the arrangement of the lower electrode layers F1 to F5 areclearly shown in FIG. 7. FIG. 7 is a top view of the flexible substrate110, and the manner how fan-shaped lower electrode layers F1 to F4 and acircular lower electrode layer F5 are arranged is clearly shown. On theother hand, the shape and the arrangement of the upper electrode layersE1 to E5 are clearly shown in FIG. 8. FIG. 8 is a bottom view of thefixed substrate 120, and the manner how fan-shaped upper electrodelayers E1 to E4 and a circular upper electrode layer E5 are arranged isclearly shown. The upper electrode layers E1 to E5 and the lowerelectrode layers F1 to F5 have the same shape, and are formed atpositions opposite to each other, respectively. Accordingly,electrostatic capacitance elements are formed by corresponding pairs ofopposite electrode layers. Eventually, five electrostatic capacitanceelements in total are formed. These electrostatic capacitance elementsare called electrostatic capacitance elements C1 to C5. For example, anelement formed by the upper electrode layer E1 and the lower electrodelayer F1 is called an electrostatic capacitance element C1.

<1.2> Oscillation Mechanism of Oscillator

Let now study what phenomenon takes place in the case where a voltage isapplied across a predetermined pair of electrodes of the sensor. First,consideration will be made in the case where a predetermined voltage isapplied across the electrode layers E1, F1. For example, as shown inFIG. 9, when a voltage is applied so that the electrode layer E1 side ispositive and the electrode layer F1 side is negative, the both electrodelayers undergo an attractive force based on Coulomb force exertedtherebetween. As previously described, flexible substrate 110 is asubstrate having flexibility. Accordingly, bending takes place by suchan attractive force. Namely, as shown in FIG. 9, the flexible substrate110 is mechanically deformed so that the distance between the electrodelayers E1, F1 across which voltage is applied is contracted. When such amechanical deformation takes place in the flexible substrate 110,oscillator 130 produces a displacement by ΔX in the positive directionof the X-axis.

Consideration will be then made in the case where a predeterminedvoltage is applied across the electrode layers E2, F2. For example, asshown in FIG. 10, when a voltage is applied so that the electrode layerE2 side is positive and the electrode F2 side is negative, theseelectrodes undergo an attractive force exerted therebetween. Thus, theflexible substrate 110 is mechanically deformed so that the distancebetween the electrode layers E2, F2 is contracted. As a result, theoscillator 130 produces a displacement by −ΔX in the negative directionof the X-axis. Eventually, when a voltage is applied across theelectrode layers E1, F1, the oscillator 130 undergoes a displacement inthe positive direction of the X-axis. On the other hand, when a voltageis applied across the electrode layers E2, F2, the oscillator 130undergoes a displacement in the negative direction of the X-axis.Accordingly, by interchangeably carrying out application of voltageacross the electrode layers E1, F1 and application of voltage across theelectrode layers E2, F2, it is possible to reciprocate the oscillator130 in the X-axis direction.

Meanwhile, as shown in FIGS. 7 and 8, the above-described electrodes E1,F1; E2, F2 are electrode layers arranged on the X-axis. On the contrary,the electrode layers E3, F3, E4, F4 are arranged on the Y-axis.Accordingly, it can be easily understood that an approach is employed tointerchangeably carry out application of voltage across the electrodelayers E3, F3 and application of voltage across the electrode layers E4,F4, it is possible to reciprocate the oscillator 130 in the Y-axisdirection.

Subsequently, consideration will be made in connection with the casewhere a predetermined voltage is applied across electrode layers E5, F5.For example, as shown in FIG. 11, when a voltage is applied so that theelectrode layer E5 side is positive and the electrode layer F5 side isnegative, these electrodes undergo an attractive force exertedtherebetween, so flexible substrate 110 is mechanically deformed so thatthe distance between the electrode layers E5, F5 is contracted. Sincethese electrode layers E5, F5 are both positioned at centers ofrespective substrates, there takes place a displacement such that theflexible substrate 110 undergoes parallel displacement in the Z-axisdirection without being inclined. As a result, the oscillator 130produces a displacement by ΔZ in the positive direction of the Z-axis.When application of voltage across the both electrode layers E5, F5 isstopped, the oscillator 130 returns to the original position (positionshown in FIG. 6). Accordingly, by intermittently carrying outapplication of voltage across the both electrode layers E5, F5, it ispossible to reciprocate the oscillator 130 in the Z-axis direction.

As stated above, when application of voltage is carried out with respectto a specific set of electrode layers at a specific timing, it ispossible to oscillate the oscillator 130 along the X-axis, the Y-axisand the Z-axis. It is to be noted that while it has been described thatvoltage is applied so that the upper electrode layers E1 to E5 side arepositive and the lower electrode layer F1 to F5 side are negative, evenif the polarity is caused to be opposite to the above, an attractiveforce is also exerted, with the result that the same phenomenon takesplace.

Eventually, in order to allow the oscillator 130 to produce oscillationUx in the X-axis direction, it is sufficient to apply a voltage V1having a waveform as shown in FIG. 12 across the electrode layers E1,F1, and to apply a voltage V2 having a waveform as shown in FIG. 12across the electrode layers E2, F2. When voltages of such waveform areapplied, a displacement ΔX as shown in FIG. 9 is produced in theoscillator 130 at time periods t1, t3, t5, and a displacement −ΔX asshown in FIG. 10 is produced in the oscillator 130 at time periods t2,t4. Similarly, in order to allow the oscillator 130 to produceoscillation Uy in the Y-axis direction, it is sufficient to apply avoltage V3 having a waveform as shown in FIG. 13 across the electrodelayers E3, F3, and to apply a voltage V4 having a waveform as shown inFIG. 13 across the electrode layers E4, F4. In order to allow theoscillator 130 to produce oscillation Uz in the Z-axis direction, it issufficient to apply a voltage V5 having a waveform as shown in FIG. 14across the electrode layers E5, F5. When voltage V5 of such a waveformis applied, a displacement ΔZ as shown in FIG. 11 is produced in theoscillator 130 at time periods t1, t3, t5, and the oscillator 130returns to the position shown in FIG. 6 by a restoring force of theflexible substrate 110 at time periods t2, t4 (At this time, adisplacement −ΔZ corresponding to an inertia force is produced).

<1.3> Mechanism for Detecting Coriolis Force

1.3.1 Coriolis Force Based on Angular Velocity ωx about the X-axis

Subsequently, the mechanism for detecting a Coriolis force exerted onthis sensor by making use of changes of electrostatic capacitance willbe described. Initially, consideration is made in connection with thephenomenon that an angular velocity ωx about the X-axis is exerted onthe sensor. For example, in the case where object 20 shown in FIG. 2 iscarrying out rotational movement at an angular velocity ωx about theX-axis, if this sensor is mounted on the object 20, angular velocity(component) ωx about the X-axis is exerted on the oscillator 130.Meanwhile, as explained with reference to FIG. 3, when the oscillator iscaused to produce oscillation Uz in the Z-axis direction in the statewhere angular velocity ωx about the X-axis is exerted, a Coriolis forceFy is produced in the Y-axis direction. Accordingly, when an approach isemployed to apply a voltage V5 having a waveform as shown in FIG. 14across the electrode layers E5, F5 of this sensor, and to allow theoscillator 130 to produce oscillation Uz in the Z-axis direction, aCoriolis force Fy must be produced in the Y-axis direction.

FIG. 15 is a side cross sectional view showing the state where amechanical deformation is produced in the flexible substrate 110 by thisCoriolis force Fy. When the oscillator 130 is oscillated in the Z-axisdirection in the state where the entirety of the sensor rotates atangular velocity ωx about the X-axis (in a direction perpendicular toplane surface of the figure), a Coriolis force Fy is produced in theY-axis direction, so a force for moving the oscillator 130 in the Y-axisdirection is applied. By this force, the flexible substrate 110 isdeformed as shown. Such deformation deviating in the Y-axis direction isnot based on Coulomb force between electrode layers, but results fromCoriolis force Fy. With respect to a voltage applied across theelectrode layers, voltage V5 as shown in FIG. 14 is only applied acrossthe electrode layers E5, F5 as described above, but any application ofvoltage is not carried out with respect to other pairs of electrodelayers. In this case, since the Coriolis force Fy produced takes a valueproportional to the angular velocity component ωx, if the value of theCoriolis force Fy can be measured, it is possible to detect the angularvelocity component ωx.

In view of this, the Coriolis force Fy is measured in accordance withthe following method by making use of a change of electrostaticcapacitance. Let now consider the distances between the upper electrodelayers E1 to E5 and the lower electrode layers F1 to F5. Since theoscillator 130 oscillates in upper and lower directions of FIG. 15,contraction and expansion of the distance between both the electrodelayers are cyclically repeated. Accordingly, the phenomenon thatcapacitance values (which are assumed to be indicated by the samereference numerals C1 to C5) of the capacitance elements C1 to C5constituted with the upper electrode layers E1 to E5 and the lowerelectrode layers F1 to F5 all cyclically increase or decrease will berepeated. However, a deformation deviating in the Y-axis directionalways will be produced in the flexible substrate 110 by action of theCoriolis force Fy. As a result, the oscillator 130 oscillates upwardlyand downwardly while such a deformed state is kept. Namely, theelectrode spacing (distance) of the capacitance element C3 is alwayssmaller than the electrode spacing (distance) of the capacitance elementC4. Between the capacitance value C3 and the capacitance value C4, therelationship expressed as C3>C4 always holds. Since a difference ΔC34between the capacitance values C3 and C4 is dependent upon the degree ofdeviation in the Y-axis direction, it provides a value indicating themagnitude of the Coriolis force Fy. In other words, the greater theCoriolis force Fy is, the greater the difference ΔC34 is.

Summary of the procedure for detecting angular velocity (component) ωxabout the X-axis described above is as follows. First, a voltage V5 of awaveform as shown in FIG. 14 is applied across the electrode layers E5,F5 to allow oscillator 130 to produce oscillation Uz in the Z-axisdirection, thus to determine a capacitance value difference ΔC34 betweenthe capacitance elements C3, C4 at that time point. The difference ΔC34determined in this way indicates a detected value of angular velocitycomponent ωx to be determined. Since the electrode layers E5, F5 usedfor producing oscillation and the electrode layers E3, F3; E4, F4 usedfor measuring capacitance value differences are electrically completelyindependent, there is no possibility that any interference may takeplace between the oscillation mechanism and the detection mechanism.

1.3.2 Coriolis Force Based on Angular Velocity ωy About the Y-axis

Let consider the phenomenon in the case where angular velocity ωy aboutthe Y-axis is exerted on this sensor. As explained with reference toFIG. 4, when the oscillator is caused to produce oscillation Ux in theX-axis direction in the state where angular velocity ωy about the Y-axisis exerted, a Coriolis force Fz is produced in the Z-axis direction.Accordingly, when an approach is employed to apply a voltage V1 and avoltage V2 having waveforms as shown in FIG. 12 across the electrodelayers E1, F1 and across the electrode layers E2, F2 of this sensor, andto allow oscillator 130 to produce oscillation Ux in the X-axisdirection, a Coriolis force Fz must be produced in the Z-axis direction.

FIG. 16 is a side cross sectional view showing the state where amechanical deformation is produced in the flexible substrate 110 by thisCoriolis force Fz. When the oscillator 130 is oscillated in the X-axisdirection in the state where the entirety of this sensor rotates at anangular velocity ωy about the Y-axis (in a direction perpendicular toplane surface of paper of the figure), a Coriolis force Fz is producedin the Z-axis direction, so a force for moving the oscillator 130 in theZ-axis direction is applied. By this force, the flexible substrate 110is deformed as shown. Such deformation deviating in the Z-axis directionis not based on Coulomb force between electrode layers, but results fromCoriolis force Fz. With respect to application of voltage acrosselectrode layers, as described above, voltages V1, V2 as shown in FIG.12 are only applied across the electrode layers E1, F1; E2, F2, but anyvoltage is not applied across other electrode layers. Since the Coriolisforce Fz produced indicates a value proportional to angular velocity ωy,if the value of the Coriolis force Fz can be measured, it is possible todetect angular velocity (component) ωy.

The value of the Coriolis force Fz can be determined on the basis ofcapacitance value C5 of the capacitance element C5 formed by the upperelectrode layer E5 and the lower electrode layer F5. This is becausethere can be obtained the relationship that according as the Coriolisforce Fz becomes greater, the distance between both the electrode layersis contracted, so the capacitance value C5 becomes greater, whereasaccording as the Coriolis force Fz becomes smaller, the distance betweenboth the electrode layers is expanded, so the capacitance value C5becomes small. It is to be noted that the oscillator 130 oscillates inthe X-axis direction, but this oscillation Ux exerts no influence onmeasurement of capacitance value C5. When the oscillator 130 produces adisplacement in a positive direction or in a negative direction of theX-axis, the upper electrode layer E5 and the lower electrode layer F5are placed in non-parallel state. However, since the distance betweenboth the electrode layers is partially contracted and is partiallyexpanded, the oscillation Ux has no influence on the capacitance valueC5 as a whole.

Summary of the procedure for detecting angular velocity component ωyabout the Y-axis described above is as follows. First, voltages V1 andV2 of waveforms as shown in FIG. 12 are applied across the electrodelayers E1, F1; E2, F2 to allow the oscillator 130 to produce oscillationUx in the X-axis direction, thus to determine a capacitance value of thecapacitance element C5 at that time point. The capacitance value C5 thusdetermined indicates a detected value of angular velocity (component) ωyto be determined. Since the electrode layers E1, F1; E2, F2 used forproducing oscillation and the electrode layers E5, F5 used for measuringa capacitance value are electrically completely independent, there is nopossibility that any interference may take place between the oscillationmechanism and the detection mechanism.

1.3.3 Coriolis Force Based on Angular Velocity ωz About the Z-axis

Finally, let consider the phenomenon in the case where angular velocitycomponent ωz about the Z-axis is exerted on this sensor. As explainedwith reference to FIG. 5, when the oscillator is caused to produceoscillation Uy in the Y-axis direction in the state where angularvelocity component ωz about the Z-axis is exerted, a Coriolis force Fxis produced in the X-axis direction. Accordingly, when an approach isemployed to apply voltages V3, V4 having waveforms as shown in FIG. 13across the electrode layers E3, F3 and across the electrode layers E4,F4 of this sensor, and to allow the oscillator 130 to produceoscillation Uy in the Y-axis direction, a Coriolis force Fx must beproduced in the X-axis direction.

FIG. 17 is a side cross sectional view showing the state where amechanical deformation is produced in the flexible substrate 110 by thisCoriolis force Fx. When the oscillator 130 is oscillated in the Y-axisdirection (in a direction perpendicular to plane surface of paper) inthe state where the entirety of this sensor rotates at angular velocityωz about the Z-axis, a Coriolis force Fx is produced in the X-axisdirection, so a force for moving the oscillator 130 in the X-axisdirection is applied. By this force, the flexible substrate 110 isdeformed as shown. Such deformation deviating in the X-axis direction isnot based on Coulomb force between electrode layers, but results fromthe Coriolis force Fx. Since this Coriolis force Fx indicates a valueproportional to the angular velocity component ωz, if the value of theCoriolis force Fx can be measured, it is possible to detect angularvelocity ωz.

This Coriolis force Fx can be measured by making use of a change ofelectrostatic capacitance similarly to the Coriolis force Fy. Namely,while the previously described Coriolis force Fy can be determined bythe difference ΔC34 between the capacitance values C3 and C4, Coriolisforce Fx can be determined by a difference ΔC12 between the capacitancevalues C1 and C2 on the basis of exactly the same principle as theabove.

Summary of the procedure for detecting angular velocity ωz about theZ-axis described above is as follows. First, an approach is employed torespectively apply voltages V3 and V4 of waveforms as shown in FIG. 13across the electrode layers E3, F3 and across the electrode layers E4,F4, and to allow the oscillator 130 to produce oscillation Uy in theY-axis direction, thus to determine a capacitance value difference ΔC12between the capacitance elements C1, C2 at that time point. Thedifference ΔC12 thus determined indicates a detected value of angularvelocity ωz to be determined. Since the electrode layers E3, F3; E4, F4used for producing oscillation and the electrode layers E1, F1; E2, F2used for measuring a capacitance value difference are electricallycompletely independent, there is no possibility that any interferencemay take place between the oscillation mechanism and the detectionmechanism.

<1.4> Circuit for Detecting Coriolis Force

As described above, in the sensor according to the first embodiment,angular velocity ωx about the X-axis is detected by determining adifference ΔC34 between capacitance values C3 and C4; angular velocityωy about the Y-axis is detected by determining capacitance value C5; andangular velocity ωz about the Z-axis is detected by determining adifference ΔC12 between capacitance values C1 and C2. In view of this,an example of a circuit suitable for measuring a capacitance value or acapacitance value difference as described above is disclosed.

FIG. 18 shows an example of a circuit for measuring capacitance value ofcapacitance element C. A signal delivered to an input terminal T1 isbranched into signals in two paths, and these signals are respectivelypassed through inverters 151 and 152. In the lower path, the signalpassed through the inverter 152 is further passed through a delaycircuit comprised of a resistor 153 and a capacitance element C,resulting in becoming one input signal of an Exclusive OR circuit 154.In the upper path, the signal passed through the inverter 151 results inbecoming the other input signal of the Exclusive OR circuit 154 as itis. A logical output of the Exclusive OR circuit 154 is delivered to anoutput terminal T2. In this example, the inverter 152 is an elementprovided for the purpose of providing sufficient drive ability withrespect to a delay circuit comprised of resistor 153 and capacitanceelement C. In addition, the inverter 151 is an element provided for thepurpose of allowing the upper and lower paths to have the samecondition, and is an element having the same operating characteristic asthat of the inverter 152.

Consideration will be made in connection with the case where when ana.c. signal of a predetermined period is delivered to the input terminalT1 in such a circuit, what signal can be obtained on the output terminalT2. FIG. 19 is a timing chart showing waveforms appearing on respectiveportions in the case where a rectangular a.c. signal of a half period fis delivered to the input terminal T1 (Although rounding occurs in arectangular wave in actual, such a waveform is indicated as a purerectangular wave for convenience of explanation) in this example. Thewaveform on the node N1, which is one input terminal of the Exclusive ORcircuit 154, is an inverted waveform delayed by a time a required forwhich a signal is passed through the inverter 151 with respect to thewaveform delivered to the input terminal T1. On the other hand, thewaveform on the node N2, which is the other input terminal of theExclusive OR circuit 154, is an inverted waveform delayed by a time intotal (a+b) of a time a required for which a signal is passed throughthe inverter 152 and a time b required for which a signal is passedthrough the delay circuit comprised of the resistor 153 and thecapacitance element C with respect to the waveform delivered to theinput terminal T1. As a result, the output waveform of the Exclusive ORcircuit 154 obtained at the output terminal T2 is a waveform having apulse width b and a period f as shown. When it is now assumed that thecapacitance value of the capacitance element C varies, any change takesplace in the delay time b of the delay circuit comprised of the resistor153 and the capacitance element C. Accordingly, the pulse width thusobtained is equal to a value indicating capacitance value of thecapacitance element C.

FIG. 20 shows an example of a circuit for measuring a difference ΔCbetween capacitance values of two capacitance elements C1, C2. A signaldelivered to an input terminal T3 is branched into signals in two paths,and these signals are respectively passed through inverters 161 and 162.In the upper path, the signal passed through the inverter 161 is furtherpassed through a delay circuit comprised of a resistor 163 and acapacitance element C1, resulting in one input signal of the ExclusiveOR circuit 165. In the lower path, the signal passed through theinverter 162 is further passed through a delay circuit comprised of aresistor 164 and a capacitance element C2, resulting in the other inputsignal of the Exclusive OR circuit 165. A logical output of theExclusive OR circuit 165 is delivered to output terminal T4. In thisexample, the inverters 161, 162 are an element provided for the purposeof providing sufficient drive ability with respect to a delay circuit ofthe succeeding stage, and the both inverters have the same operatingcharacteristic.

Let now consider what signal can be obtained at an output terminal T4 inthe case where an a.c. signal of a predetermined period is delivered tothe input terminal T3 in such a circuit. As shown in FIG. 21, when arectangular a.c. signal is delivered to input terminal T3, the waveformon node N3, which is one input terminal of the Exclusive OR circuit 165,is an inverted waveform having a predetermined delay time d1. Similarly,the waveform on node N4, which is the other input terminal, is aninverted waveform having a predetermined delay time d2. As a result, theoutput waveform of the Exclusive OR circuit 165 obtained at the outputterminal T4 is a waveform having a pulse width d as shown. Here, thepulse width d is a value corresponding to a difference between delaytimes d1 and d2, and takes a value corresponding to difference ΔCbetween capacitance values of the two capacitance elements C1, C2. Thus,the capacitance value difference ΔC can be obtained as pulse width d.

<1.5> Modification 1

In the above-described sensor according to the first embodiment, anattractive force based on Coulomb force is exerted to the oscillateoscillator 130. For example, in the case of oscillating the oscillator130 in the X-axis direction, it is sufficient that the first state wherecharges having polarities opposite to each other are delivered to boththe electrode layers E1, F1 so that an attractive force is exertedtherebetween as shown in FIG. 9 and the second state where chargeshaving polarities opposite to each other are delivered to both theelectrode layers E2, F2 so that an attractive force is exertedtherebetween as shown in FIG. 10 are repeated reciprocally. However, inorder to still more stabilize such an oscillation, it is preferable toexert a repulsive force along with an attractive force. When an approachis employed, as shown in FIG. 22, for example, to respectively deliverpositive and negative charges to the upper electrode layer E1 and thelower electrode layer F1 to allow both the electrode layers to undergoan attractive force exerted therebetween, and to deliver negativecharges to both the upper electrode layer E2 and the lower electrodelayer F2 (or to deliver positive charges to both the electrodes) toallow both the electrode layers to undergo a repulsive force exertedtherebetween, it is possible to carry out, in more stable manner, theoperation for allowing the oscillator 130 to undergo displacement by ΔXin the positive direction of the X-axis. The state shown in FIG. 9 andthe state shown in FIG. 22 are the same in that the oscillator 130 iscaused to undergo displacement ΔX. However, the former is dependent upona force exerted on one portion, whereas the latter is dependent upon aforce exerted on two portions. Therefore, the latter is more stable thanthe former.

Similarly, as shown in FIG. 10, also in the case where the oscillator130 is caused to undergo displacement by −ΔX in the negative directionof the X-axis, when an approach is employed, as shown in FIG. 23, torespectively deliver positive charges and negative charges to the upperelectrode layer E2 and the lower electrode layer F2 to allow both theelectrode layers to undergo an attractive force exerted therebetween,and to deliver negative charges to both the upper electrode layer E1 andthe lower electrode layer F1 (or to deliver positive charges to both theelectrodes) to allow both the electrode layers to undergo a repulsiveforce exerted therebetween, the operation can be still more stabilized.Eventually, when an approach is employed to deliver charges of apredetermine polarity to respective electrode layers at a predeterminedtiming so that the first state shown in FIG. 22 and the second stateshown in FIG. 23 are repeated reciprocally, it is possible to oscillatethe oscillator 130 in the X-axis direction in a stable manner. Also inthe case of oscillating the oscillator 130 in the Y-axis direction, itsoperation is exactly the same as the above.

Let consider the case where the oscillator 130 is oscillated in theZ-axis direction. In the previously described embodiment, the firststate where positive charges and negative charges are respectivelydelivered to the upper electrode layer E5 and the lower electrode layerF5 to allow both the electrode layers to undergo an attractive forceexerted therebetween as shown in FIG. 11 and the neutral state where nocharge is delivered to any electrode layer are repeated reciprocally sothat oscillation Uz is produced. Also in this case, by making use of arepulsive force between both electrode layers, the operation can be morestabilized. Namely, when an approach is employed as shown in FIG. 24 todeliver positive charges to both the upper electrode layer E5 and thelower electrode layer F5 (or to deliver negative charges to both theelectrode layers) to allow both the electrode layers to undergo arepulsive force exerted therebetween, the oscillator 130 produces adisplacement −ΔZ in the negative direction of the Z-axis. In view ofthis, when an approach is employed to deliver, at a predeterminedtiming, charges of a predetermined polarity to respective electrodelayers so that the first state shown in FIG. 11 and the second stateshown in FIG. 24 are repeated reciprocally, it becomes possible tooscillate the oscillator 130 in a stabilized manner in the Z-axisdirection.

While it is possible to easily deliver charges of polarities opposite toeach other to a pair of opposite electrode layers, it is necessary tomake a particular device in order to deliver charges of the samepolarity. Namely, it is sufficient to apply a predetermined voltageacross both electrode layers in order to deliver charges of polaritiesopposite to each other, but such a method cannot be applied in order todeliver charges of the same polarity. To solve this problem, there maybe employed a method in which respective electrode layers are caused tobe of a double layer structure through dielectric substance. FIG. 25 isa side cross sectional view of a sensor employing such a structure.Lower electrode layers F1 to F5 are formed on the upper surface of adielectric substrate 171, and auxiliary electrode layers F1 a to F5 aare formed between the dielectric substrate 171 and the flexiblesubstrate 110. The auxiliary electrode layers F1 a to F5 a have the sameshape as that of the lower electrode layers F1 to F5, and are arrangedat the same positions, respectively. Similarly, upper electrode layersE1 to E5 are formed on the lower surface of a dielectric substrate 172,and auxiliary electrode layers E1 a to E5 a are formed between thedielectric substrate 172 and the fixed substrate 120. The auxiliaryelectrode layers E1 a to E5 a have the same shape as that of the upperelectrode layers E1 to E5 and are arranged at the same positions,respectively.

If such a double layer structure is employed, it is possible to allowspecific electrode layers to undergo an attractive force exertedtherebetween, or to allow them to undergo a repulsive force exertedtherebetween without constraint. This is indicated by using an actualexample. FIG. 26 is a view showing only extracted portions of respectiveelectrode layers and respective dielectric substrates in the sensorshown in FIG. 25. For example, in the case where there is a desire toallow the electrode layers E1, F1 to undergo an attractive force exertedtherebetween, it is sufficient to apply a voltage V across both theelectrode layers so that charges of polarities opposite to each otherare delivered thereto. On the contrary, in the case where there is adesire to allow the electrode layers E2, F2 to undergo a repulsive forceexerted therebetween, it is sufficient to apply a voltage across theauxiliary substrates E2 a, F2 a and across the electrode layers E2, F2as shown. Since voltage V is applied with the dielectric substrate 171being put between the auxiliary electrode layer and the electrode layer,negative charges are produced in the electrode layer F2 and positivecharges are produced in the auxiliary electrode layer F2 a. Similarly,since voltage V is applied with the dielectric substrate 172 being putbetween the auxiliary electrode layer and the electrode layer, negativecharges are produced in the electrode layer E2 and positive charges areproduced in the auxiliary electrode layer E2 a. In this way, charges ofthe same polarity are delivered as a result to both the electrode layersE2, F2. Thus, both the electrode layers are permitted to undergo arepulsive force exerted therebetween.

<1.6> Modification 2

The above-described modification 1 somewhat becomes complex in structurethan the sensor shown in FIG. 6. On the contrary, modification 2described below is directed to a sensor in which the structure of thesensor shown in FIG. 6 is more simplified. Namely, in the sensor of themodification 2, as shown in FIG. 27, a single common electrode layer E0is formed in place of the upper electrode layers E1 to E5. This commonelectrode layer E0 is a disk-shaped electrode layer having suchdimensions to face all of the lower electrode layers F1 to F5. Even ifelectrode layers on one side are formed as a single common electrodelayer as stated above, when a potential on this common electrode layerside is always taken as a reference potential, no obstruction takesplace in the operation of this sensor. For example, in the case ofapplying a voltage across a specific pair of electrode layers in orderto allow the oscillator 130 to produce oscillation, it is sufficientthat the common electrode layer E0 side is grounded to deliver a voltageto a predetermined electrode layer of the lower electrode layers F1 toF5. Further, also in the case of detecting Coriolis force on the basisof change of capacitance value, it is sufficient that the commonelectrode layer E0 side is similarly grounded to handle respectivecapacitance elements C1 to C5.

As stated above, the five upper electrode layers E1 to E5 are replacedby the single common electrode layer E0, thereby permitting mechanicalstructure of the sensor and/or necessary wiring thereof to be moresimple. Further, if fixed substrate 120 is constituted with a conductivematerial such as metal, etc., the lower surface of the fixed substrate120 can be used as the common electrode layer E0. For this reason, thenecessity of purposely forming the common electrode layer E0 as aseparate body on the lower surface of the fixed substrate 120 iseliminated. Thus, the structure becomes simpler.

While the example where the upper electrode layers E1 to E5 sides arereplaced by the common electrode layer E0 has been described, the lowerelectrode layers F1 to F5 sides may be replaced by a common electrodelayer F0 in a manner opposite to the above.

§2 Second Embodiment

<2.1> Structure of Sensor According to Second Embodiment

Subsequently, a multi-axial angular velocity sensor according to asecond embodiment of this invention will be described. This secondembodiment is also the same as the above-described sensor of the firstembodiment in that a mechanism utilizing Coulomb's force is used as theoscillating mechanism and a mechanism utilizing change of electrostaticcapacitance is used as the detecting mechanism. It should be noted thatits structure is comprised of a plurality of substrates stacked, and istherefore more suitable for mass production.

FIG. 28 is a side cross sectional view of the multi-axial angularvelocity sensor according to the second embodiment. This sensorincludes, as its main components, a first substrate 210, a secondsubstrate 220, and a third substrate 230. In this embodiment, the firstsubstrate 210 is comprised of a silicon substrate, and the second andthird substrates 220 and 230 are comprised of a glass substrate.Respective substrates are connected to each other by anodic bonding. Thefirst substrate 210 is a substrate serving as the center role of thissensor. FIG. 29 is a top view of the first substrate 210. As clearlyshown in FIG. 29, L-shaped opening portions H1 to H4 are provided in thefirst substrate 210. Respective opening portions H1 to H4 have a tapershape such that the widths become broader according as the positionsthereof shift in a lower direction. The side cross sectional view cutalong cutting lines 28—28 in FIG. 29 is FIG. 28, and the side crosssectional view cut along the cutting lines 30—30 is FIG. 30. The crosssections in a taper shape of opening portions H3, H4 are shown in FIG.30. In FIG. 29, the inside square portions encompassed by the fourL-shaped opening portions H1 to H4 constitute an oscillator 211, and theoutside portions of the L-shaped opening portions H1 to H4 constitute asupport frame 213 with respect to the oscillator 211. The oscillator 211is connected at four portions with respect to the support frame 213.These four connecting portions serve as a bridging portion 212. In otherwords, the square oscillator 211 is in hanging state by the bridgingportions 212 at four portions. In addition, as shown in FIG. 28 or 30,the bridging portion 212 is a member in a very small thin plate form ascompared to the original thickness of the first substrate 210, thusproviding flexibility. For this reason, the oscillator 211 can move witha certain degree of freedom in the state where it is hung by thebridging portions 212. On the upper surface of the oscillator 211, asshown in FIG. 29, five lower electrode layers G1 to G5 are formed. Theselower electrode layers G1 to G5 perform, similarly to the lowerelectrode layers F1 to F5 in the previously described sensor of thefirst embodiment, the function for allowing the oscillator 211 to beoscillated and the function for detecting a Coriolis force exerted onthe oscillator 211.

A second substrate 220 functions as a pedestal for supporting theperipheral portion of the first substrate 210. To realize this, a recess221 is formed at the portions except for the peripheral portion of theupper surface of the second substrate 220. By formation of this recess221, the oscillator 211 can be kept in a hanging state without being incontact with the second substrate 220.

A third substrate 230 functions as a cover for covering the uppersurface of the first substrate 210. The bottom view of the thirdsubstrate 230 is shown in FIG. 31. The lower surface of the thirdsubstrate 230 is dug except for a small portion therearound, and anupper electrode layer G0 is formed on the dug surface 231. The upperelectrode layer G0 is square, and is placed in the state where it isfaced to all the lower electrode layers G1 to G5 as indicated by theside cross sectional view of FIG. 28 or FIG. 30. This lower electrodelayer G0 corresponds to the common electrode layer E0 of the sensor ofFIG. 27 shown as modification 2 in the previously described firstembodiment.

Such sensors comprised of three substrates are suitable for massproduction. Namely, machining (or chemical processing such as etching,etc.) may be individually implemented to respective substratesthereafter to form electrode layers or wiring layers to connect andcombine them. If a silicon substrate is used as the first substrate 210,the electrode layers G1 to G5 may be formed by a diffused layer.Further, the electrode layer G0 may be formed with a vacuum depositionlayer such as aluminum. In this way, electrode layers or wiring layersmay be formed by general semiconductor planar process.

<2.2> Mechanism for Oscillating Oscillator

The sensor of this embodiment is the same as the previously describedsensor of the first embodiment in that an approach is employed to applya predetermined voltage, at a predetermined timing, to the five lowerelectrode layers G1 to G5 formed on the oscillator 211 and the upperelectrode layer G0 opposite thereto to thereby allow both the electrodelayers to undergo Coulomb's force therebetween, thus making it possibleto oscillate the oscillator 211 in a predetermined direction. It is tobe noted that arrangement of electrode layers of the sensor of thesecond embodiment and that of the previously described sensor of thefirst embodiment are somewhat different. In the sensor of the firstembodiment, as shown in FIG. 7, the electrode layers F1, F2 are disposedon the X-axis and the electrode layers F3, F4 are disposed on theY-axis. On the contrary, in the sensor of the second embodiment whichwill be described below, as shown in FIG. 29, the electrode layers G1 toG4 are all not disposed on the X-axis or the Y-axis. Namely, theelectrode layers G1 to G4 are respectively arranged in first to fourthquadrants with respect to the XY plane. For this reason, a method ofapplying a voltage required for oscillating the oscillator 211 in aspecific direction is somewhat different from that of the previouslydescribed example. This voltage application method will now be describedin a more practical manner.

In order to oscillate the oscillator 211 in the X-axis direction, thefollowing method is adopted. It is now assumed that a potential on theupper electrode layer G0 is caused to be earth potential as a referencepotential, and a predetermined voltage (e.g., +5V) is applied to thelower electrode layers G1 to G5. First, when voltages of +5 volts arerespectively applied to both the lower electrode layers G1 and G4, it iseasily understood that the electrode layers G1, G0 and the electrodelayers G4, G0 are caused to respectively undergo attractive forceexerted therebetween. Thus, the oscillator 211 is brought into the statewhere a displacement ΔX takes place in a positive direction of theX-axis. Then, potentials on the lower electrode layers G1, G4 are causedto be a reference potential for a second time and voltages of +5 voltsare respectively applied to both the lower electrode layers G2 and G3.As a result, the electrode layers G2, G0 and the electrode layers G3 andG0 are caused to respectively undergo attractive force exertedtherebetween. Thus, the oscillator 211 is brought into the state where adisplacement −ΔX takes place in a negative direction of the X-axis. Whena predetermined voltage is applied to respective electrode layers at apredetermined timing so that these two states are repeated one afteranother, it becomes possible to oscillate the oscillator 211 in theX-axis direction.

In the case of oscillating the oscillator 211 in the Y-axis direction,an operation similar to the above is conducted. First, when voltages of+5 volts are respectively applied to both the lower electrode layers G1and G2, it is easily understood that the electrode layers G1, G0 and theelectrode layers G2, G0 are caused to undergo attractive force exertedtherebetween, respectively. Thus, the oscillator 211 is brought into thestate where displacement ΔY takes place in a positive direction of theY-axis. Then, potentials on the lower electrode layers G1, G2 are causedto be a reference potential for a second time and voltages of +5 voltsare respectively applied to both the lower electrode layers G3 and G4.As a result, the electrode layers G3, G0 and the electrode layers G4, G0are caused to respectively undergo attractive force exertedtherebetween. Thus, the oscillator 211 is brought into the state wheredisplacement −ΔY takes place in a negative direction of the Y-axis. Whena predetermined voltage is applied to respective electrode layers at apredetermined timing so that the above-mentioned two states are repeatedone after another, it becomes possible to oscillate the oscillator 211in the Y-axis direction.

In addition, in order to oscillate the oscillator 211 in the Z-axis, itis sufficient to employ the same method as that of the above-describedsensor of the first embodiment. Namely, it is enough to repeatedly carryout an operation to apply +5 volts to the lower electrode layer G5, orto allow an applied voltage to be 0 volts for a second time.

<2.3> Mechanism for Detecting Coriolis Force

In the sensor according to the second embodiment, the principle fordetecting Coriolis force exerted on the oscillator 211 resides inutilization of change of electrostatic capacitance similarly to thepreviously described sensor according to the first embodiment. However,since there is a slight difference in the arrangement of electrodelayers, there is a slight difference in combination of capacitanceelements used as a detecting element. The combination of capacitanceelements will now be described in a more practical sense. It is hereassumed that five sets of capacitance elements constituted bycombination of the lower electrode layers G1 to G5 and the upperelectrode layer G0 are respectively called capacitance elements C1 to C5for convenience of explanation, and capacitance values of thesecapacitance elements are similarly called C1 to C5.

A method of detecting Coriolis force Fx exerted in the X-axis will befirst studied. In accordance with the electrode layer arrangement shownin FIG. 29, it can be easily imagined that when Coriolis force Fx in thepositive direction of the X-axis is applied to the oscillator 211, theelectrode layer spacing between the capacitance elements C1, C4 iscontracted and the electrode layer spacing between the capacitanceelements C2, C3 is broadened. Accordingly, capacitance values C1, C4increase, whereas capacitance values C2, C3 decrease. Then, if adifference of (C1+C4)−(C2+C3) is obtained, this difference takes a valuecorresponding to the Coriolis force Fx.

A method of detecting a Coriolis force Fy exerted in the Y-axisdirection will now be studied. In accordance with the electrode layerarrangement shown in FIG. 29, it can be easily imagined that whenCoriolis force Fy in the positive direction of the Y-axis is applied tothe oscillator 211, the electrode layer spacing between the capacitanceelements C1, C2 is contracted, whereas the electrode layer spacingbetween the capacitance elements C3, C4 is broadened. Accordingly,capacitance values C1, C2 increase, whereas capacitance values C3, C4decrease. Then, if a difference of (C1+C2)−(C3+C4) is obtained, thisdifference takes a value corresponding to Coriolis force Fy.

A method of detecting a Coriolis force Fz exerted in the Z-axisdirection is the same as the detecting method in the previouslydescribed sensor of the first embodiment. Namely, a capacitance value C5of the capacitance element C5 takes a value indicating Coriolis forceFz.

It is to be noted that, in the sensor of this embodiment, since the sameelectrode layers are used at the same time for both the oscillatingmechanism and the detecting mechanism, it is required that a voltagesupply circuit for producing oscillation and a circuit for detecting acapacitance value varying on the basis of Coriolis force do notinterfere with each other.

<2.4> Modification 1

A sensor shown in FIG. 32 is a modification of the sensor according tothe second embodiment shown in FIG. 28. In this modification, a fourthsubstrate 240 is further used in addition to the first substrate 210,the second substrate 220 and the third substrate 230. The fourthsubstrate 240 is constituted by an oscillator 241 and a pedestal 242.The oscillator 241 is a block in a square form when viewed from the top,and the pedestal 242 is a frame in such a form to surround the peripherythereof. The oscillator 241 of the fourth substrate is connected to theoscillator 211 of the first substrate, and these oscillators 211 and 241function as a single oscillator as a whole. By adding fourth substrate240 in this way, mass of oscillator can be increased. Thus, detection ofhigher sensitivity can be made. It is to be noted that, in thismodification, five upper electrode layers G6 to G10 are provided inplace of providing the common upper electrode layer G0 as electrodelayers opposite to the five lower electrode layers G1 to G5.

<2.5> Modification 2

A sensor shown in FIG. 33 is another modification of the sensoraccording to the second embodiment shown in FIG. 28. The substratefunctioning as the center of this sensor is a flexible substrate 250.FIG. 34 is a top view of this flexible substrate 250. As indicated bybroken lines in the figure, an annular groove is formed at the lowersurface of the flexible substrate 250. Since the portion where suchgroove is formed has a thin thickness, it has flexibility (which isindicated as a flexible portion 252 in FIG. 33). It is now assumed thatthe inside portion encompassed by the annular flexible portion 252 iscalled a working portion 251 and the outside portion of the flexibleportion 252 is called a fixed portion 253. On the lower surface of theworking portion 251, an oscillator 260 in a block form is fixed.Further, the fixed portion 253 is supported by a pedestal 270 and thepedestal 270 is fixed on a base substrate 280. Eventually, theoscillator 260 is placed in hanging state within a space encompassed bythe pedestal 270. Since the flexible portion 252 with a thin thicknesshas flexibility, the oscillator 260 can undergo displacement within thisspace with a certain degree of freedom. Further, a cover substrate 290is attached at the upper portion of the flexible substrate 250 in such amanner to cover it while keeping a predetermined space.

As shown in FIG. 34, five lower electrode layers F1 to F5 are formed onthe upper surface of flexible substrate 250. These electrode layers havethe same shape and the same arrangement as those of the lower electrodelayers F1 to F5 in the sensor according to the first embodiment shown inFIG. 6. Further, a common upper electrode layer E0 opposite to all thefive lower electrode layers F1 to F5 is formed on the lower surface ofthe cover substrate 290. It is to be noted that since the operation ofthis sensor is equivalent to the operation of the sensor shown in FIG.27, the detailed explanation is omitted here.

§3 Third Embodiment

<3.1> Structure of Sensor According to Third Embodiment

Subsequently, a multi-axial angular velocity sensor according to thethird embodiment of this invention will be described. While the thirdembodiment is the same as the previously described sensors of the firstand second embodiments in that mechanism utilizing Coulomb's force isused as an oscillating mechanism, it is characterized in that mechanismutilizing a piezo resistance element is used as a detecting mechanism.

FIG. 35 is a side cross sectional view of the multi-axial angularvelocity sensor according to the third embodiment. This sensor includes,as major components, a first substrate 310, a second substrate 320, athird substrate 330, and a fourth substrate 340. In this embodiment, thefirst and third substrates 310 and 330 are constituted with siliconsubstrate, and the second and fourth substrates 320 and 340 areconstituted with a glass substrate. Such structure comprised of fourlayers of substrates is substantially the same as the modification shownin FIG. 32 in the previously described second embodiment. The firstsubstrate 310 is a substrate which performs the role serving as thecenter of this sensor, and FIG. 36 is a top view of the first substrate310. As indicated by broken lines in the figure, an annular groove isformed at the lower surface of the first substrate 310. Since theportion where this groove is formed has a thin thickness, it hasflexibility (which is indicated as a flexible portion 312 in FIG. 35).It is now assumed that the inside portion encompassed by the annularflexible portion 312 is called a working portion 311 and the outsideportion of the flexible portion 312 is called a fixed portion 313. Thesecond substrate 320 is constituted with an oscillator 321 in a blockform and a pedestal 322 in a frame form to surround the peripherythereof. The oscillator 321 is fixed on the bottom surface of theworking portion 311. Further, the pedestal 322 is fixed on the bottomsurface of the fixed portion 313.

A third substrate 330 performs the role as a base substrate forsupporting the pedestal 322. To realize this, at the portion except forthe periphery on the upper surface side of the third substrate 330, arecess 331 is formed. By formation of this recess 331, the oscillator321 is supported without being in contact with the third substrate 330.Eventually, the oscillator 321 is in hanging state within a spaceencompassed by the pedestal 322. Since the flexible portion 312 with athin thickness has flexibility in the first substrate 310, theoscillator 321 can undergo displacement within this space with a certaindegree of freedom. Further, a fourth substrate 340 is attached at theupper part of the first substrate 310 in a manner to cover it whilekeeping a predetermined space.

As shown in FIG. 36, five lower electrode layers F1 to F5 are formed onthe upper surface of the first substrate 310. These electrode layers areequivalent to the lower electrode layers F1 to F5 in the sensoraccording to the first embodiment shown in FIG. 6. It is to be notedthat, as described later, a plurality of piezo resistance elements R areformed on the upper surface of the first substrate 310, and the shape oflower electrode layers F1 to F4 is somewhat different from the shape ofthe lower electrode layers F1 to F4 in the sensor shown in FIG. 6 so asto avoid the region where these piezo resistance elements R are formed.Further, a common upper electrode layer E0 face to all the five lowerelectrode layers F1 to F5 is formed on the lower surface of the fourthsubstrate 340.

Piezo resistance elements R are an element formed by injecting impurityat predetermined positions on the upper surface side of the firstsubstrate 310 comprised of silicon, and have the property that electricresistance varies by action of mechanical stress. As shown in FIG. 36,twelve piezo resistance elements R in total, that is, four elementsalong the X-axis, four elements along the Y-axis, and four elementsalong an oblique axis inclined at 45 degrees relative to the Y-axis arearranged. All elements are arranged on the flexible portion 312 havingthin thickness. When bending takes place in the flexible portion 312 bydisplacement of the oscillator 321, resistance values of thepiezo-resistance elements vary in correspondence with this bending. Itis to be noted that, in the side cross sectional view of FIG. 35,indication of these piezo resistance elements R is omitted for avoidanceof complexity of the figure. It is now assumed that, as shown in FIG.37, with respect to these twelve resistance elements, four resistanceelements arranged along the X-axis are called Rx1, Rx2, Rx3, Rx4, fourresistance elements arranged along the Y-axis are called Ry1, Ry2, Ry3,Ry4, and four resistance elements arranged along the oblique axis arecalled Rz1, Rz2, Rz3, Rz4.

<3.2> Mechanism for Oscillating Oscillator

In this sensor, the mechanism for oscillating the oscillator 321 in apredetermined axis direction is exactly the same as that of the sensoraccording to the first embodiment shown in FIG. 6. The five lowerelectrode layers F1 to F5 shown in FIG. 36 is completely equivalent tothe five lower electrode layers F1 to F5 shown in FIG. 7 in point of theessential function although the shape is somewhat different.Accordingly, by applying a predetermined voltage to the five lowerelectrode layers F1 to F5 and the common upper electrode layer E0opposite thereto at a predetermined timing, Coulomb's force is appliedacross both the electrode layers, thus making it possible to oscillatethe oscillator 321 in any direction of the X-axis, the Y-axis and theZ-axis in the XYZ three-dimensional coordinate system.

<3.3> Mechanism for Detecting Coriolis Force

The feature of the sensor according to this third embodiment resides inthat detection of Coriolis force is carried out by using piezoresistance elements. This detecting method will now be described. Letnow consider the case where a Coriolis force Fx in the positivedirection of the X-axis is applied to the oscillator 321 as shown inFIG. 38 (indication of respective electrode layers is omitted in thisfigure for the purpose of avoiding complexity of the figure). WhenCoriolis force Fx is applied, bending as shown in the figure takes placein the flexible portion 312 of the first substrate 310. Such a bendingvaries resistance values of the four piezo-resistance elements Rx1 toRx4 arranged along the X-axis. In actual terms, resistance values of thepiezo resistance elements Rx1, Rx3 increase (indicated by “+” sign inthe figure), whereas resistance values of the piezo resistance elementsRx2, Rx4 decrease (indicated by “−” sign in the figure). In addition,the degree of increase/decrease is proportional to the magnitude ofCoriolis force Fx applied. On the other hand, in the case where Coriolisforce −Fx in the negative direction of the X-axis is applied, therelationship of increase/decrease is inverted. Accordingly, if changesof resistance values of respective piezo resistance elements aredetected, it is possible to determine the applied Coriolis force Fx.

In more practical sense, a bridge circuit as shown in FIG. 39 is formedby the four piezo resistance elements Rx1 to Rx4 to apply apredetermined voltage by using a power supply 350. Then, a bridgevoltage Vx is measured by a voltage meter 361. Here, in the referencestate where no Coriolis force is applied (the state shown in FIG. 35),when setting is made such that the bridge circuit is equilibrated(bridge voltage Vx becomes equal to zero), bridge voltage Vx measured bythe voltage meter 361 indicates Coriolis force Fx.

On the other hand, when Coriolis force Fy in the Y-axis direction isapplied, similar resistance value changes take place with respect to thefour piezo resistance elements Ry1 to Ry4 arranged along the Y-axis.Accordingly, when a bridge circuit as shown in FIG. 40 is formed bythese four piezo resistance elements to deliver a predetermined voltageby using a power supply 350, a bridge voltage Vy measured by a voltagemeter 362 indicates Coriolis force Fy.

Further, when Coriolis force Fz in the Z-axis direction is applied,resistance value changes take place with respect to the four piezoresistance elements Rz1 to Rz4 arranged along the oblique axis. Forexample, when Coriolis force in the positive direction of the Z-axis isapplied, resistance values of the piezo resistance elements Rz1, Rz4decrease, whereas resistance values of the piezo resistance elementsRz2, Rz3 increase. Accordingly, when a bridge circuit as shown in FIG.41 is formed by these four piezo resistance elements to deliver apredetermined voltage by using a power supply 350, a bridge voltage Vzmeasured by a voltage meter 363 indicates Coriolis force Fz.

When detection of Coriolis force is carried out by using piezoresistance elements in this way, the mechanism for oscillating theoscillator 321 in a predetermined axial direction (utilizing Coulomb'sforce between electrode layers) and the mechanism for detecting Coriolisforce are completely independent. Thus, there is no possibility thatthey may interfere with each other.

<3.4> Modification

Respective lower electrode layers F1 to F4 in the above-described sensorare arranged on the X-axis and the Y-axis similarly to the previouslydescribed sensor of the first embodiment. On the contrary, as in thelower electrode layers G1 to G4 in the sensor according to the secondembodiment shown in FIG. 29, they may be arranged in the first to fourthquadrants with respect to the XY plane. Further, the four piezoresistance elements Rz1 to Rz4 may be arranged in any axial direction,e.g., may be arranged along the axis in parallel to the X-axis orY-axis.

§4 Fourth Embodiment

<4.1> Structure of Sensor According to the Fourth Embodiment

A multi-axial angular velocity sensor according to the fourth embodimentof this invention will now be described. The fourth embodiment isdirected to a sensor using piezoelectric elements for both theoscillating mechanism and the detecting mechanism.

FIG. 42 is a side cross sectional view of the multi-axial angularvelocity sensor according to the fourth embodiment. This sensor has astructure very similar to the sensor according to the first embodimentshown in FIG. 6, and comprises respective components as described below.Namely, fundamentally, this sensor is of a structure such that, betweena disk-shaped flexible substrate 410 and a disk-shaped fixed substrate420, a piezoelectric element 430 similarly disk-shaped is inserted. Onthe lower surface of the flexible substrate 410, a columnar oscillator440 is fixed. Further, the outer circumferential portion of the flexiblesubstrate 410 and the outer circumferential portion of the fixedsubstrate 420 are both supported by a sensor casing 450. On the uppersurface of the piezoelectric element 430, five upper electrode layers E1to E5 (only a portion thereof is indicated in FIG. 42) are formed.Similarly, on the lower surface thereof, five lower electrode layers F1to F5 (only a portion thereof is similarly indicated) are formed. Theupper surfaces of the upper electrode layers E1 to E5 are fixed on thelower surface of the fixed substrate 420, and the lower surfaces of thelower electrode layers F1 to F5 are fixed on the upper surface of theflexible substrate 410. In this example, the fixed substrate 420 has asufficient rigidity to such a degree that no bending takes place. On theother hand, the flexible substrate 410 has flexibility and functions asso called diaphragm. Let now consider an XYZ three-dimensionalcoordinate system using gravity position O of the oscillator 440 as theorigin. Namely, an X-axis is defined in a right direction in the figure,as a Z-axis is defined in an upper direction, and a Y-axis is defined ina direction perpendicular to the plane surface of paper. FIG. 42 is across sectional view cut along the XZ plane of this sensor. It is to benoted that shape and arrangement of the upper electrode layers E1 to E5and the lower electrode layers F1 to F5 are exactly the same as those ofthe sensor of the first embodiment shown in FIG. 6 (see FIGS. 7 and 8).Further, in this embodiment, the flexible substrate 410 and the fixedsubstrate 420 are both constituted by insulating material. In the caseof attempting to constitute these substrates with conductive materialsuch as metal, etc., it is sufficient to provide insulating filmsbetween these substrates and respective electrode layers so that therespective electrode layers are not short-circuited with each other.

Generally, a piezoelectric element has the first property that whenpressure is applied thereto from the external, a voltage is produced ina predetermined direction within the piezoelectric element and thesecond property that when voltage is applied thereto from the external,pressure is produced in a predetermined direction within thepiezoelectric element in a manner opposite to the above. These twoproperties have the reverse of each other. The relationships betweendirections in which pressure/voltage is applied and directions in whichvoltage/pressure is produced are inherent in individual piezoelectricelements. Here, the property of such directivity is called “polarizationcharacteristic”. The piezoelectric element 430 used in the sensor ofthis embodiment has a polarization characteristic as shown in FIGS.43(a) and 43(b). Namely, when considered from the view-point of thepreviously described first property, the piezoelectric element has apolarization characteristic such that in the case where a force toexpand in a thickness direction is applied as shown in FIG. 43(a),positive charges and negative charges are respectively produced on theupper electrode layer E side and on the lower electrode layer F side,while in the case where a force to contract in the thickness directionis applied as shown in FIG. 43(b), negative charges and positive chargesare respectively produced on the upper electrode layer E side and on thelower electrode layer F side. When considered from a view-point of thesecond property in a manner opposite to the above, the piezoelectricelement has a polarization characteristic such that when positivecharges and negative charges are respectively delivered to the upperelectrode layer E side and the lower electrode layer F side as shown inFIG. 43(a), a force to expand in the thickness direction is produced,while when negative charges and positive charges are respectivelydelivered to the upper electrode layer E side and the lower electrodelayer F side, a force to contract in the thickness direction is producedas shown in FIG. 43(b).

<4.2> Mechanism for Oscillating Oscillator

Let now study what phenomenon takes place in the case where chargeshaving a predetermined polarity are delivered to a predeterminedelectrode layer of this sensor. When negative charges and positivecharges are respectively delivered to the electrode layer E1 and F1, aforce to contract in a thickness direction is produced at a portion ofthe piezoelectric element 430 put between both the electrode layers bythe property shown in FIG. 43(b). On the other hand, when positivecharges and negative charges are respectively delivered to the electrodelayers E2, F2, a force to expand in a thickness direction is produced ata portion of the piezoelectric element 430 put between both theelectrode layers by the property shown in FIG. 43(a). As a result, thepiezoelectric element 430 is deformed as shown in FIG. 44 and theoscillator 440 is caused to undergo displacement in the positivedirection of the X-axis. Now, when the polarity of charges which havebeen delivered to the electrode layers E1, F1, E2, F2 is inverted, theexpanding/contracting state of the piezoelectric element 430 is alsoinverted. Thus, the oscillator 440 is caused to undergo displacement inthe negative direction of the X-axis. When an approach is employed tointerchangeably invert the polarity of charges delivered so that thesetwo displacement states take place one after another, it is possible toreciprocate the oscillator 440 in the X-axis direction. In other words,the oscillator 440 is permitted to undergo oscillation Ux with respectto the X-axis direction.

Such charge supply can be realized by applying an a.c. signal acrossopposite electrode layers. Namely, a first a.c. signal is applied acrossthe electrode layers E1, F1, and a second a.c. signal is applied acrossthe electrode layers E2, F2. If signals having the same frequency andphases opposite to each other are used as the first and second a.c.signals, the oscillator 440 can be oscillated in the X-axis direction.

A method of allowing the oscillator 440 to undergo oscillation Uy withrespect to the Y-axis direction is also exactly the same. Namely, it issufficient to apply a first a.c. signal across the electrode layers E3,F3, and to apply a second a.c. signal across the electrode layers E4,F4.

Let now consider a method of allowing the oscillator 440 to undergooscillation Uz with respect to the Z-axis direction. Assuming now thatnegative charges and positive charges are respectively delivered to theelectrode layers E5, F5, a force to contract in a thickness direction isproduced at a portion of the piezoelectric element 430 put between boththe electrode layers. As a result, the piezoelectric element 430 isdeformed as shown in FIG. 45 and the oscillator 440 is caused to undergodisplacement in the positive direction of the Z-axis. When the polarityof charges which have been delivered to the electrode layers E5, F5 isinverted, the expanding/contracting state of the piezoelectric element430 is also inverted. Thus, the oscillator 440 is caused to undergodisplacement in the negative direction of the Z-axis. If the polarity ofcharges delivered is reciprocally inverted so that these twodisplacement states take place one after another, the oscillator 440 canbe reciprocated in the Z-axis direction. In other words, the oscillatoris permitted to undergo oscillation Uz with respect to the Z-axisdirection. Such charge supply can be realized by applying an a.c. signalacross the opposite electrode layers E5, F5.

As stated above, if a predetermined a.c. signal is delivered to aspecific set of electrode layers, it is possible to oscillate theoscillator 430 along the X-axis, the Y-axis and the Z-axis.

<4.3> Mechanism for Detecting Coriolis Force

Subsequently, a method of detecting Coriolis force components exerted inrespective axial directions in the sensor according to the fourthembodiment will be described. It is to be noted that, for the purpose ofsaving paper, FIGS. 44 and 45 which were used for explanation of thepreviously described method of oscillating the oscillator are used alsoin the explanation of the method of detecting Coriolis force.

First, let consider the case where Coriolis force Fx in the X-axisdirection is applied to the oscillator 440 as shown in FIG. 44 (Inaccordance with the principle shown in FIG. 5, since measurement of suchCoriolis force Fx is carried out in the state caused to undergooscillation Uy in the Y-axis direction, the oscillator 440 is assumed tobe oscillated in a direction perpendicular to plane surface of paper inFIG. 44, but such oscillating phenomenon in the Y-axis direction has noinfluence on measurement of Coriolis force Fx in the X-axis direction).By action of such Coriolis force Fx, bending is produced in the flexiblesubstrate 410 performing the function of diaphragm, so a force tocontract in thickness direction is exerted at the right half of thepiezoelectric element 430, and a force to expand in thickness directionis exerted at the left half. Also in the case where Coriolis force Fy inthe Y-axis direction is exerted, the direction of the axis is onlyshifted by 90 degrees, but a phenomenon similar to the above is to takeplace. In addition, in the case where Coriolis force in the Z-axisdirection is exerted, the piezoelectric element 430 undergoes a force tocontract in thickness direction as a whole as shown in FIG. 45.

When a pressure as described above is applied to the piezoelectricelement 430, charges of a predetermined polarity are produced atrespective electrode layers by the property shown in FIGS. 43(a) and43(b). Accordingly, if charges thus produced are detected, a Coriolisforce applied can be detected. In more practical sense, wirings as shownin FIGS. 46 to 48 are implemented to respective electrode layers,thereby making it possible to detect applied Coriolis force componentsFx, Fy, Fz. For example, Coriolis force component Fx in the X-axisdirection can be detected as voltage difference Vx produced betweenterminals Tx1 and Tx2 as shown in FIG. 46. It is possible to easilyunderstand the reason when consideration is made in connection with thepolarity of charges produced at respective electrode layers. Namely,with respect to the electrode layers E2, F2, since a portion of thepiezoelectric element 430 put therebetween is subject to a force toexpand in a thickness direction, positive charges and negative chargesare respectively produced at the upper electrode layer E2 and the lowerelectrode layer F2 as shown in FIG. 43(a). On the other hand, withrespect to the electrode layers E1, F1, since a portion of thepiezoelectric element 430 put therebetween is subject to a force tocontract in thickness direction, negative charges and positive chargesare respectively produced at the upper electrode layer E1 and the lowerelectrode layer F1 as shown in FIG. 43(b). Accordingly, when a wiring asshown in FIG. 46 is implemented, positive charges are all gathered atterminal Tx1 and negative charges are all gathered at terminal Tx2.Thus, a potential difference Vx across both terminals indicates Coriolisforce Fx. Entirely in the same manner, when a wiring as shown in FIG. 47is implemented to the upper electrode layers E3, E4 and the lowerelectrode layers F3, F4, it is possible to detect Coriolis force Fy inthe Y-axis direction as a potential difference Vy across terminals Ty1and Ty2. In addition, it is possible to detect a Coriolis force Fz inthe Z-axis direction as a potential difference Vz produced acrossterminals Tz1 and Tz2 as shown in FIG. 48. The reason can be easilyunderstood when consideration is made in connection with polarity ofcharges produced at respective electrode layers by bending as shown inFIG. 45. Namely, with respect to the electrode layers E5, F5, since aportion of the piezoelectric element 430 put therebetween is subject toa force to contract in thickness direction, negative charges andpositive charges are respectively produced at the upper electrode layerE5 and the lower electrode layer F5 as shown in FIG. 43(b). Accordingly,when such a wiring to gather positive charges at terminal Tz1 and togather negative charges at terminal Tz2 is implemented as shown in FIG.48, a potential difference Vz across both terminals indicates Coriolisforce Fz in the Z-axis direction.

<4.4> Detection of Angular Velocity

The object of the multi-axial angular velocity sensor according to thisinvention resides in that as explained in §0, in order to detect anangular velocity ω about a first axis, an oscillator is allowed toundergo oscillation U in a second axis direction to detect a Coriolisforce F produced in a third axis direction at that time. As describedabove, in the sensor according to the fourth embodiment, an a.c. signalis applied across a predetermined pair of electrode layers, therebymaking it possible to oscillate the oscillator 430 along any axialdirection of the X-axis, the Y-axis and the Z-axis, and to respectivelydetect Coriolis force components Fx, Fy, Fz in respective axesdirections produced at that time as potential differences Vx, Vy, Vz.Accordingly, by the principle shown in FIGS. 3 to 5, it is possible todetect an angular velocity ω about any axis of the X-axis, the Y-axisand the Z-axis.

It should be noted that, in the sensor according to this embodiment, apiezoelectric element is used for both the oscillating mechanism and thedetecting mechanism. In other words, the same electrode layer mayperform the role for delivering charges for producing oscillation (therole as the oscillating mechanism), or may perform the role fordetecting charges produced by Coriolis force (role as the detectingmechanism). With the same electrode layer, it is relatively difficult topermit these two roles to be performed at the same time. However, inthis sensor, since sharing of roles as described below is made withrespect to respective electrode layers, there is no possibility that tworoles may be given to the same electrode layer at the same time.

Let first consider the operation for detecting angular velocity ω aboutthe X-axis on the basis of the principle shown in FIG. 3. In this case,it is necessary to detect a Coriolis force Fy produced in the Y-axisdirection when an oscillator is caused to undergo oscillation Uz in theZ-axis direction. In the sensor shown in FIG. 42, in order to allow theoscillator 430 to undergo oscillation Uz, it is sufficient to apply ana.c. signal across the electrode layers E5, F5. Further, in order todetect Coriolis force Fy exerted on the oscillator 430, it is sufficientto detect charges produced at the electrode layers E3, F3, E4, F4 asshown in the circuit diagram of FIG. 47. The remaining electrode layersE1, F1, E2, F2 are not used in this detecting operation.

Subsequently, let consider the operation for detecting angular velocityωy about the Y-axis on the basis of the principle shown in FIG. 4. Inthis case, it is necessary to detect a Coriolis force Fz produced in theZ-axis direction when an oscillator is caused to undergo oscillation Uxin the X-axis direction. In the sensor shown in FIG. 42, in order toallow the oscillator 430 to undergo oscillation Ux, it is sufficient toapply a.c. signals having phases opposite to each other across theelectrode layers E1, F1 and across the electrode layers E2, F2. Further,in order to detect Coriolis force Fz exerted on the oscillator 430, itis sufficient to detect charges produced at the electrode layers E5, F5as shown in the circuit diagram of FIG. 48. The remaining electrodelayers E3, F3, E4, F4 are not used in this detecting operation.

Finally, let consider the operation for detecting an angular velocity ωzabout the Z-axis on the basis of the principle shown in FIG. 5. In thiscase, it is necessary to detect Coriolis Fx produced in the X-axisdirection when an oscillator is caused to undergo oscillation Uy in theY-axis direction. In the sensor shown in FIG. 42, in order to allow theoscillator 430 to undergo oscillation Uy, it is sufficient to apply a.c.signals having phases opposite to each other across the electrode layersE3, F3 and across the electrode layers E4, F4. Further, in order todetect Coriolis force Fx exerted on the oscillator 430, it is sufficientto detect charges produced at the electrode layers E1, F1, E2, F2 asshown in the circuit diagram of FIG. 46. The remaining electrode layersE5, F5 are not used in this detecting operation.

It is seen that in the case of detecting any one of angular velocitiesωx, ωy, ωz by using this sensor as stated above, sharing of roles withrespect to respective electrode layers is conveniently carried out sothat detection can be carried out without hindrance. It should be notedthat since it is unable to detect plural ones of angular velocities ωx,ωy, ωz, in the case where an attempt is made to detect three angularvelocity components, it is required to carry out time-divisionprocessing as described later to sequentially carry out detections oneby one.

<4.5> Modification 1

In accordance with the above-described sensor according to the fourthembodiment, it is possible to detect Coriolis force components Fx, Fy,Fz in the XYZ three-dimensional coordinate system as potentialdifferences Vx, Vy, Vz, respectively. Thus, detection of angularvelocity can be made on the basis of these potential differences.However, in order to detect these potential differences, it is necessaryto implement wirings as shown in the circuit diagrams of FIGS. 46 to 48to respective electrode layers. Such wirings are such that upperelectrode layers and lower electrode layers are mixed. Accordingly, inthe case of mass-producing such sensors, the cost for wiring is notnegligible as compared to the total cost of product. In thismodification 1, the polarization characteristic of a piezoelectricelement is partially varied, thereby simplifying wiring to reduce themanufacturing cost.

Generally, it is possible to manufacture piezoelectric elements havingan arbitrary polarization characteristic by the present technology. Forexample, the piezoelectric element 430 used in the above-describedsensor according to the fourth embodiment had a polarizationcharacteristic as shown in FIGS. 43(a) and 43(b). On the other hand, itis also possible to manufacture a piezoelectric element 460 having apolarization characteristic as shown in FIGS. 49(a) and 49(b). Namely,this piezoelectric element 460 has a polarization characteristic suchthat in the case where a force to expand in thickness direction isapplied as shown in FIG. 49(a), negative charges and positive chargesare respectively produced on the upper electrode layer E side and on thelower electrode layer F side, while when a force to contract inthickness direction is applied as shown in FIG. 49(b), positive chargesand negative charges are respectively produced on the upper electrodelayer E side and on the lower electrode layer F side. It is now assumedthat, for convenience, polarization characteristic as shown in FIGS.43(a) and 43(b) is called type I and polarization characteristic asshown in FIGS. 49(a) and 49(b) is called type II. The piezoelectricelement 430 having polarization characteristic of the type I and thepiezoelectric element 460 having polarization characteristic of the typeII are such that signs of charges produced on the upper surface side andon the lower surface side are inverted. It should be noted that sinceupsetting of the piezoelectric element 430 results in the piezoelectricelement 460, it can be said that both the piezoelectric elements areexactly the same piezoelectric element when viewed as a single body.Therefore, it is not so significant to discriminate between both thepiezoelectric elements. However, there may be employed a configurationsuch that a portion of one piezoelectric element is caused to havepolarization characteristic of the type I and another portion thereof iscaused to have polarization characteristic of the type II. Themodification described below is characterized in that a piezoelectricelement to which such a localized polarization processing is implementedis used to thereby simplify the structure of a multi-axial angularvelocity sensor.

Let now consider a piezoelectric element 470 as shown in FIG. 50. Thispiezoelectric element 470 is a disk-shaped element which is exactly thesame in shape as the piezoelectric element 430 used in theabove-described sensor of FIG. 42, but its polarization characteristicis different from that of the piezoelectric element 430. Thepiezoelectric element 430 was an element in which all portions havepolarization characteristic of the type I as previously described. Onthe contrary, the piezoelectric element 470 has a polarizationcharacteristic of either the type I or the type II in five regions A1 toA5 as shown in FIG. 50. Namely, this piezoelectric element indicatespolarization characteristic of the type I in regions A2, A4 andindicates polarization characteristic of the type II in regions A1, A3,A5. In this example, regions A1 to A5 correspond to regions where theupper electrode layers E1 to E5 or the lower electrode layers F1 to F5are respectively formed.

Let now consider what polarities of charges produced on respectiveelectrode layers in the case where the piezoelectric element 470 havinglocalized polarization characteristic as shown in FIG. 50 is used inplace of the piezoelectric element 430. It is thus understood thatpolarities of charges produced at the upper electrode layers E1, E3, E5and the lower electrode layers F1, F3, F5 provided in the region havingpolarization characteristic of the type II is inverted with respect tothe sensor using the piezoelectric element 430. For this reason, whenwirings as shown in FIGS. 51 to 53 are implemented to the respectiveelectrode layers, it is possible to determine Coriolis force componentsFx, Fy, Fz as potential differences Vx, Vy, Vz, respectively. Forexample, with respect to Coriolis force Fx in the X-axis direction,since polarities of charges produced at the electrode layers E1, F1 areinverted with respect to the previously described example, the wiringshown in FIG. 46 is replaced by the wiring shown in FIG. 51. Similarly,with respect to Coriolis force Fy in the Y-axis direction, sincepolarities of charges produced at the electrode layers E3, F3 areinverted, the wiring shown in FIG. 47 is replaced by the wiring shown inFIG. 52. Further, with respect to Coriolis force Fz in the Z-axisdirection, since polarities of charges produced at the electrode layersE5, F5 are inverted, the wiring shown in FIG. 48 is replaced by thewiring shown in FIG. 53.

It is to be noted that in the case where the piezoelectric element 470having localized polarization characteristic is used, the polarity of ana.c. signal applied for oscillating the oscillator 430 must be varied asoccasion demands. Namely, it is understood that in the case where thepiezoelectric element 470 having a localized polarization characteristicis used, when a.c. signals having the same phase are applied across theelectrode layers E1, F1 formed in the region A1 and the electrode layersE2, F2 formed in the region A2, it is possible to oscillate theoscillator 430 in the X-axis direction, and when a.c. signals having thesame phase are similarly applied across the electrode layers E3, F3formed in the region A3 and the electrode layers E4, F4 formed in theregion A4, it is possible to oscillate the oscillator 430 in the Y-axisdirection.

The wirings shown in FIGS. 51 to 53 have significant merits inmanufacturing actual sensors as compared to the wirings shown in FIGS.46 to 48. The feature of the wirings shown in FIGS. 51 to 53 resides inthat even in the case where a Coriolis force in any direction of theX-axis, the Y-axis and the Z-axis is applied, if Coriolis force isapplied in the positive direction of each axis, positive charges andnegative charges are necessarily produced on the upper electrode layerside and on the lower electrode layer side. By making use of thisfeature, the wiring of the entirety of sensor can be simplified. Forexample, let consider the case where terminals Tx2, Ty2, Tz2 in FIGS. 51to 53 are connected to the sensor casing 450 to allow those terminals tohave a reference potential (earth). In this case, the five lowerelectrode layers F1 to F5 are brought into the state where they areconductive with each other. Even if such an approach is employed,potential difference Vx indicating Coriolis force Fx in the X-axisdirection is obtained as a voltage with respect to the earth of terminalTx1, potential difference Vy indicating Coriolis force Fy in the Y-axisdirection is obtained as a voltage with respect to the earth of terminalTy1, and potential difference Vz indicating Coriolis force Fz in theZ-axis direction is obtained as a voltage with respect to the earth ofterminal Tz1. Accordingly, this sensor operates without any hindrance.In addition, since wirings with respect to the five lower electrodelayers F1 to F5 are caused to conduct with each other, wiring can becomevery simple.

<4.6> Modification 2

In the case where the piezoelectric element 470 having localizedpolarization characteristic as described in the above-describedmodification 1, it is possible to provide wiring which allows the fivelower electrode layers F1 to F5 to be conductive. If the lower electrodelayers F1 to F5 are permitted to be conductive in this way, there is nonecessity of intentionally allowing these five electrode layers to beindependent electrode layers, respectively. Namely, as shown in the sidecross sectional view of FIG. 54, it is sufficient to provide only onecommon lower electrode layer F0. The common lower electrode layer F0 isa single disk-shaped electrode layer, and serves as an electrodeopposite to all of five upper electrode layers E1 to E5.

<4.7> Modification 3

In order to further simplify the structure of the above-described secondembodiment, it is sufficient to use a flexible substrate 480 comprisedof a conductive material (e.g., metal) in place of flexible substrate410. If such a substrate is employed, it is possible to realize thestructure in which the lower surface of the piezoelectric element 470 isdirectly connected to the upper surface of the flexible substrate 480,without using special lower electrode layer F0 as shown in the sidecross sectional view of FIG. 55. In this case, the flexible substrate480 itself functions as common lower electrode layer F0.

Further, while the lower electrode layer side is caused to be a commonsingle electrode layer in the above-described modifications 2, 3, theupper electrode layer side may be a common single electrode layer in amanner opposite to the above.

<4.8> Other Modifications

While the above-described sensors all use physically singlepiezoelectric element 430 or 470, they may be comprised of physicallyplural piezoelectric elements. For example, in FIG. 50, there may beemployed a configuration in which respective regions A1 to A5 areconstituted individual piezoelectric elements, and five piezoelectricelements in total are used. As stated above, how many piezoelectricelements are used from a physical point of view is the manner which canbe suitably changed in design.

Further, while the outer peripheral portions of flexible substrates 410,480 are supported by sensor casing 450 in the above-described sensor, itis not necessarily required to fix a flexible substrate to a sensorcasing. For example, there may be employed, as shown in FIG. 56, aconfiguration in which a flexible substrate 490 having a slightlysmaller diameter is used in place of flexible substrate 480 and theperiphery of flexible substrate 490 is allowed to be the end of freedom.

§5 Fifth Embodiment

<5.1> Structure of Sensor According to Fifth Embodiment

A multi-axial angular velocity sensor according to the fifth embodimentof this invention will now be described. The fifth embodiment is alsodirected to a sensor using a piezoelectric element for both theoscillating mechanism and the detecting mechanism similarly to thepreviously described fourth embodiment.

FIG. 57 is a top view of the multi-axial angular velocity sensoraccording to the fifth embodiment. Flexible substrate 510 is adisk-shaped substrate having flexibility which functions as so calleddiaphragm. On the flexible substrate 510, so called a doughnutdisk-shaped piezoelectric element 520 is disposed. On the upper surfaceof the piezoelectric element 520, sixteen upper electrode layers L1 toL16 in forms as shown in the figure are formed at positions shown,respectively. Further, on the lower surface of the piezoelectric element520, sixteen lower electrode layers M1 to M16 (although not shown inFIG. 57) having exactly the same shapes as those of the upper electrodelayers L1 to L16 are formed at positions respectively opposite to theupper electrode layers L1 to L16. FIG. 58 is a side cross sectional viewof this sensor (For the purpose of avoiding complexity of the figure,only cross sectional portions are illustrated with respect to respectiveelectrode layers. This similarly applies to side cross sectional viewsmentioned below). As clearly shown in this figure, the doughnut diskshaped piezoelectric element 520 is in so called a sandwich state whereit is put between sixteen upper electrode layers L1 to L16 (only L1 toL4 are shown in FIG. 58) and sixteen lower electrode layers M1 to M16(only M1 to M4 are shown in FIG. 58). The lower surfaces of the lowerelectrode layers M1 to M16 are fixed on the upper surface of theflexible substrate 510. On the other hand, an oscillator 550 is fixed onthe lower surface of the flexible substrate 510, and the peripheralportion of the flexible substrate 510 is fixedly supported by sensorcasing 560. In this embodiment, the flexible substrate 510 isconstituted by an insulating material. In the case where flexiblesubstrate 510 is constituted with a conductive material such as metal,an insulating film is formed on the upper surface thereof, therebypreventing sixteen lower electrode layers M1 to M16 from beingshort-circuited.

Here, for convenience of explanation, let consider an XYZthree-dimensional coordinate system in which the central position of theflexible substrate 510 is allowed to be origin. Namely, in FIG. 57, anX-axis is defined in a right direction, a Y-axis is defined in a lowerdirection, and a Z-axis is defined in a direction perpendicular to theplane surface of paper. FIG. 58 is a cross sectional view cut along theXZ plane of this sensor, and flexible substrate 510, piezoelectricelement 520, respective electrode layers L1 to L16, M1 to M16 are allarranged in parallel to the XY plane (In the fifth embodiment, forconvenience of explanation, the lower direction in the side crosssectional view is taken as the positive direction of the Z-axis).Further, as shown in FIG. 57, on the XY plane, a W1-axis and a W2-axisare defined in directions to form an angle of 45 degrees relative to theX-axis or the Y-axis. These W1-axis and W2-axis are both passed throughthe origin O. When such a coordinate system is defined, upper electrodelayers L1 to L4 and lower electrode layers M1 to M4 are arranged inorder from the negative direction toward the positive direction of theX-axis, upper electrode layers L5 to L8 and lower electrode layers M5 toM8 are arranged in order from the negative direction toward the positivedirection of the Y-axis, upper electrode layers L9 to L12 and lowerelectrode layers M9 to M12 are arranged in order from the negativedirection toward the positive direction of the W1-axis, and upperelectrode layers L13 to L16 and lower electrode layers M13 to M16 arearranged in order from the negative direction toward the positivedirection of the W2-axis.

As previously described, there is the property that when electrodelayers are respectively formed on the upper and lower surfaces of apiezoelectric element to apply a predetermined voltage across such apair of electrode layers, a predetermined pressure is produced withinthe piezoelectric element, while when a predetermined force is appliedto the piezoelectric element, a predetermined voltage is produced acrossthe pair of electrode layers. In view of this, it is now assumed thatsixteen sets of localized elements D1 to D16 are provided by theabove-described sixteen upper electrode layers L1 to L16, theabove-described sixteen lower electrode layers M1 to M16, and sixteenportions of the piezoelectric element 520 put between those electrodelayers. For example, a localized element D1 is provided by upperelectrode layer L1, lower electrode layer M1, and a portion ofpiezoelectric element 520 put therebetween. Eventually, sixteen sets oflocalized elements D1 to D16 are arranged as shown in the top view ofFIG. 59.

In this example, as piezoelectric element 520 in this sensor, apiezoelectric ceramics having a polarization characteristic as shown inFIGS. 60(a) and 60(b) is used. Namely, this piezoelectric ceramics has apolarization characteristic such that in the case where a force toexpand along the XY-plane is applied as shown in FIG. 60(a), positivecharges and negative charges are respectively produced on the upperelectrode layer L side and on the lower electrode layer M side, while inthe case where a force to contract along the XY-plane is applied asshown in FIG. 60(b), negative charges and positive charges arerespectively produced on the upper electrode layer L side and the lowerelectrode layer M side. Here, such a polarization characteristic iscalled type III. Sixteen sets of localized elements D1 to D16 in thissensor all have a piezoelectric element having the polarizationcharacteristic of the type III.

<5.2> Mechanism for Oscillating Oscillator

Subsequently, let study what phenomenon takes place in the case wherecharges having a predetermined polarity are delivered to a predeterminedpair of electrode layers of this sensor. Let now consider the case wherecharges of polarities as shown in FIG. 61 are delivered to respectiveelectrode layers constituting four localized elements D1 to D4 arrangedon the X-axis. Namely, positive charges and negative charges aredelivered to electrode layers L1, M2, L3, M4 and electrode layers M1,L2, M3, L4, respectively. Thus, localized elements D1 and D3 expandalong the XY-plane by the property shown in FIG. 60(a). On the contrary,localized elements D2 and D4 contract along the XY-plane by the propertyshown in FIG. 60(b). As a result, the flexible substrate 510 is deformedas shown in FIG. 61, and the oscillator 550 is caused to undergodisplacement in the positive direction of the X-axis. Now, whenpolarities of charges which have been delivered to respective electrodelayers are inverted, the expanding/contracting state of thepiezoelectric element is also inverted. Thus, the oscillator 550 iscaused to undergo displacement in the negative direction of the X-axis.If the polarities of charges delivered are reciprocally inverted so thatsuch two displacement states take place one after another, it ispossible to reciprocate the oscillator 550 in the X-axis direction. Inother words, the oscillator 550 is permitted to undergo oscillation Uxwith respect to the X-axis direction.

Such supply of charges can be realized by applying an a.c. signal acrossopposite electrode layers. Namely, a first a.c. signal is applied acrosselectrode layers L1, M1 and across electrode layers L3, M3, and a seconda.c. signal is applied across electrode layers L2, M2 and acrosselectrode layers L4, M4. If signals having the same frequency and phasesopposite to each other are used as the first and second a.c. signals, itis possible to oscillate the oscillator 550 in the X-axis direction.

A method of allowing the oscillator 550 to undergo oscillation Uy withrespect to the Y-axis direction is exactly the same as above. Namely, afirst a.c. signal is applied across electrode layers L5, M5 and acrosselectrode layers L7, M7, and a second a.c. signal is applied acrosselectrode layers L6, M6 and across electrode layers L8, M8. If signalshaving the same frequency and phases opposite to each other are used asthe first and second a.c. signals, it is possible to oscillate theoscillator 550 in the Y-axis direction.

Consideration will be described in connection with a method of allowingthe oscillator 550 to undergo oscillation Uz with respect to the Z-axisdirection. Let now consider the case where charges of polarities asshown in FIG. 62 are delivered to respective electrode layersconstituting four localized elements D9 to D12 arranged on the W1-axis.Namely, positive charges and negative charges are delivered to electrodelayers L9, M10, M11, L12 and electrode layers M9, L10, L11 M12,respectively. Thus, localized elements D9 and D12 expand along theXY-plane by the property shown in FIG. 60(a). On the contrary, localizedelements D10 and D11 contract along the XY-plane by the property shownin FIG. 60(b). As a result, the flexible substrate 510 is deformed asshown in FIG. 62, and the oscillator 550 is caused to undergodisplacement in the positive direction of the Z-axis. Now, whenpolarities of charges which have been delivered to respective electrodelayers are inverted, the expanding/contracting state of thepiezoelectric element is also inverted, so the oscillator 550 is causedto undergo displacement in the negative direction of the Z-axis. Ifpolarities of charges delivered are reciprocally inverted so that suchtwo displacement states take place one after another, it is possible toreciprocate the oscillator 550 in the Z-axis direction. In other words,the oscillator 550 can be caused to undergo oscillation Uz with respectto the Z-axis direction.

Such supply of charges can be also realized by applying an a.c. signalacross opposite electrode layers. Namely, a first a.c. signal is appliedacross electrode layers L9, M9 and across electrode layers L12, M12, anda second a.c. signal is applied across electrode layers L10, M10 andacross electrode layers L11, M11. If signals having the same frequencyand phases opposite to each other are used as the first and second a.c.signals, it is possible to oscillate the oscillator 550 in the Z-axisdirection.

As shown in FIG. 59, this sensor is further provided with four localizedelements D13 to D16 along the W2-axis. Although these four localizedelements are not necessarily required, they are provided for the purposeof allowing oscillating operation in the Z-axis to be more stable andenhancing, to more degree, the detection accuracy of Coriolis force Fzin the Z-axis direction which will be described later. These fourlocalized elements D13 to D16 perform exactly the same functions of theabove-described four localized elements D9 to D12. Namely, if a.c.signals which are the same as those delivered to localized elements D9to D12 are delivered to localized elements D13 to D16, it is possible tocarry out oscillating operation in the Z-axis direction by eightlocalized elements D9 to D16. Thus, more stable oscillating operationcan be conducted.

As stated above, if a predetermined a.c. signal is delivered to specificlocalized elements, it is possible to oscillate the oscillator 550 alongthe X-axis, the Y-axis and the Z-axis.

<5.3> Mechanism for Detecting Coriolis Force

Subsequently, a method of detecting Coriolis force components exerted inrespective axes directions in the sensor according to the fifthembodiment will now be described. It is to be noted that, for thepurpose of saving paper, FIGS. 61 and 62 used for explaining the methodof oscillating the previously described oscillator are used in theexplanation of the method of detecting this Coriolis force.

First, let consider the case where Coriolis force Fx in the X-axisdirection is applied to a center of gravity G of the oscillator 550 asshown in FIG. 61 (In accordance with the principle shown in FIG. 5,since such a measurement of Coriolis force Fx is carried out in thestate where oscillation Uy in the Y-axis direction is given, theoscillator 550 is assumed to be oscillating in a direction perpendicularto the plane surface of paper in FIG. 61, but such oscillatingphenomenon in the Y-axis direction does not affect measurement ofCoriolis force Fx in the X-axis direction). By action of such Coriolisforce Fx, bending takes place in the flexible substrate 510 whichperforms the function of diaphragm. Thus, a deformation as shown in FIG.61 takes place. As a result, localized elements D1, D3 arranged alongthe X-axis expand in the X-axis direction, and localized elements D2, D4similarly arranged on the X-axis contract in the X-axis direction. Sincethe piezoelectric element put between these respective electrode layershas a polarization characteristic as shown in FIGS. 60(a) and 60(b),charges of polarity indicated by sign “+” or “−” encompassed by smallcircle in FIG. 61 are produced in these respective electrode layers.Further, in the case where Coriolis force Fy in the Y-axis direction isapplied, charges of predetermined polarities are produced similarly withrespect to respective electrode layers constituting localized elementsD5 to D8 arranged along the Y-axis.

Let now consider the case where Coriolis force Fz in the Z-axisdirection is applied. In this case, the flexible substrate 510 whichperforms the function of diaphragm is deformed as shown in FIG. 62,localized elements D9, D12 arranged along the W1-axis expand in theW1-axis direction, and localized elements D10, D11 arranged along theW1-axis contract in the W1-axis direction. For this reason, charges ofpolarities as indicated by sign “+” or “−” encompassed by small circlein FIG. 62 are produced in respective electrode layers constitutinglocalized elements D9 to D12. Similarly, charges of predeterminedpolarities are produced also in respective electrode layers constitutinglocalized elements D13 to D16 arranged along the W2-axis.

By making use of such a phenomenon, wirings as shown in FIGS. 63 to 65are implemented to respective electrode layers, thereby making itpossible to carry out detection of Coriolis force components Fx, Fy, Fz.For example, it is possible to detect Coriolis force Fx in the X-axisdirection as a voltage difference Vx produced between terminals Tx1 andTx2 as shown in FIG. 63. It is possible to easily understand this reasonwhen consideration is made in connection with polarities of chargesproduced in respective electrode layers by bending as shown in FIG. 61.When a wiring as shown in FIG. 63 is implemented, positive charges areall gathered at terminal Tx1, and negative charges are all gathered atterminal Tx2. Thus, a potential difference Vx across both terminalsindicates Coriolis force Fx in the X-axis direction. Entirely in thesame manner, when a wiring as shown in FIG. 64 is implemented torespective electrode layers constituting localized elements D5 to D8, itis possible to detect Coriolis force Fy in the Y-axis direction as apotential difference Vy across terminals Ty1 and Ty2. Further, when awiring as shown in FIG. 65 is implemented to respective electrode layersconstituting localized elements D9 to D16, it is possible to detectCoriolis force Fz in the Z-axis direction as a voltage difference Vzproduced across terminals Tz1 and Tz2. It should be noted that localizedelements D13 to D16 are not necessarily required, but even if only fourlocalized elements D9 to D12 are used, detection of Coriolis force Fz inthe Z-axis direction can be made.

<5.4> Detection of Angular Velocity

As described above, in the multi-axial angular velocity sensor accordingto the fifth embodiment, an a.c. signal is applied across apredetermined pair of localized elements, thereby making it possible tooscillate the oscillator 550 along any axial direction of the X-axis,the Y-axis, and the Z-axis, and to detect Coriolis force components Fx,Fy, Fz in respective axes directions produced at that time as potentialdifferences Vx, Vy, Vz, respectively. Accordingly, by the principleshown in FIGS. 3 to 5, it is possible to detect an angular velocity ωabout any axis of the X-axis, the Y-axis and the Z-axis.

It is to be noted that, in the sensor according to the fifth embodiment,piezoelectric elements (localized elements) is used for both theoscillating mechanism and the detecting mechanism similarly to thepreviously described sensor according to the fourth embodiment. In viewof this, let study sharing of roles of respective localized elements inthe detecting operations of respective angular velocities.

First, let consider the operation for detecting angular velocity ωxabout the X-axis on the basis of the principle shown in FIG. 3. In thiscase, it is necessary to detect Coriolis force Fy produced in the Y-axisdirection when an oscillator is caused to undergo oscillation Uz in theZ-axis. In order to allow the oscillator 550 to undergo oscillation Uz,it is sufficient to deliver an a.c. signal to localized elements D9 toD16 arranged on the W1-axis and the W2-axis. Further, in order to detectCoriolis force Fy applied to the oscillator 550, it is sufficient todetect voltages produced at localized elements D5 to D8 arranged on theY-axis. The remaining localized elements D1 to D4 are not used in thisdetecting operation.

Subsequently, let consider the operation for detecting angular velocityωy about the Y-axis on the basis of the principle shown in FIG. 4. Inthis case, it is necessary to detect Coriolis force Fz produced in theZ-axis direction when an oscillator is caused to undergo oscillation Uxin the X-axis direction. In order to allow the oscillator 550 to undergooscillation Ux, it is sufficient to deliver an a.c. signal to localizedelements D1 to D4 arranged on the X-axis. Further, in order to detectCoriolis force Fz applied to the oscillator 550, it is sufficient todetect voltages produced at localized elements D9 to D16 arranged on theW1-axis and the W2-axis. The remaining localized elements D5 to D8 arenot used in this detecting operation.

Finally, let consider the operation for detecting angular velocity ωzabout the Z-axis on the basis of the principle shown in FIG. 5. In thisinstance, it is necessary to detect Coriolis force Fx produced in theX-axis direction when an oscillator is caused to undergo oscillation Uyin the Y-axis direction. In order to allow the oscillator 550 to undergooscillation Uy, it is sufficient to deliver an a.c. signal to localizedelements D5 to D8 arranged on the Y-axis. Further, in order to detectCoriolis force Fx applied to the oscillator 550, it is sufficient todetect voltages produced at localized elements D1 to D4 arranged on theX-axis. The remaining localized elements D9 to D16 are not used in thisdetecting operation.

As described above, it is seen that in the case of detecting any one ofangular velocity components ωx, ωy, ωz by using this sensor, sharing ofthe role with respect to respective localized elements is convenientlycarried out, so detection is carried out without hindrance. It should benoted that since it is unable to detect plural ones of angular velocitycomponents ωx, ωy, ωz at the same time, in the case where an attempt ismade to detect three angular velocity components, it is necessary toconduct time-division processing as described later to sequentiallycarry out detections one by one.

<5.5> Modification 1

In accordance with the above-described sensor of the fifth embodiment,it is possible to determine Coriolis force components Fx, Fy, Fz in theXYZ three-dimensional coordinate system as potential differences Vx, Vy,Vz, respectively. Further, it is possible to detect angular velocitycomponents on the basis of these potential differences. However, inorder to detect these potential differences, it is necessary toimplement wirings as shown in the circuit diagrams of FIGS. 63 to 65 torespective electrode layers. Such wirings are such that upper electrodelayers and lower electrode layers are mixed. Therefore, in the case ofmass-producing such sensors, the cost for wiring cannot be neglected ascompared to the total cost of product. This modification 1 ischaracterized in that the polarization characteristic of thepiezoelectric is partially varied, thereby simplifying wiring to reducethe manufacturing cost.

As previously described, it is possible to manufacture piezoelectricelements having an arbitrary polarization characteristic by the presenttechnology. For example, the piezoelectric element 520 used in theabove-described sensor according to the fifth embodiment had apolarization characteristic of the type III as shown in FIGS. 60(a) and60(b). On the contrary, it is also possible to manufacture piezoelectricelement 530 having a polarization characteristic of the type IV as shownin FIGS. 66(a) and 66(b). Namely, it is possible to manufacturepiezoelectric element 530 having a polarization characteristic such thatin the case where a force in a direction to expand along the XY plane isapplied as shown in FIG. 66(a), negative charges and positive chargesare respectively produced on the upper electrode layer L side and on thelower electrode layer M side, while in the case where a force in adirection to contract along the XY plane is applied as shown in FIG.66(b), positive charges and negative charges are respectively producedon the upper electrode layer L side and on the lower electrode layer Mside. Further, it is possible to allow a portion of one piezoelectricelement to have polarization characteristic of the type III and to allowanother portion to have polarization characteristic of the type IV. Inthe modification described below, a piezoelectric element to which sucha localized polarization processing is implemented is used to therebysimplify the structure of the sensor.

Let now consider piezoelectric element 540 as shown in FIG. 67. Thispiezoelectric element 540 is a doughnut disk shaped element which isentirely the same in shape as the piezoelectric element 520 used in theabove-described sensor of FIG. 57. However, its polarizationcharacteristic is different from that of the piezoelectric element 520.The piezoelectric element 520 was an element in which all portions havepolarization characteristic of the type III as previously described. Onthe contrary, the piezoelectric element 540 has polarizationcharacteristic of either the type III or the type IV in respectivesixteen regions as shown in FIG. 67. Namely, this piezoelectric element540 indicates polarization characteristic of the type III in the regionsof localized elements D1, D3, D5, D7, D9, D12, D13, D16, and indicatespolarization characteristic of the type IV in the regions of localizedelements D2, D4, D6, D8, D10, D11, D14, D15 (see FIGS. 59 and 67).

When consideration is now made as to how polarities of charges producedat respective electrode layers vary in the case where the piezoelectricelement 540 having polarization characteristic as shown in FIG. 67 isused in place of the piezoelectric element 520, it is seen thatpolarities of charges produced at upper electrode layers L2, L4, L6, L8,L10, L11, L14, L15 and lower electrode layers M2, M4, M6, M8, M10, M11,M14, M15 are inverted. For example, in the case where Coriolis force Fxin the X-axis direction is applied, charges of polarities as shown inFIG. 61 are produced in the previously described sensor of FIG. 57,whereas charges of polarities as shown in FIG. 68 are produced in thesensor of this modification. Further, in the case where Coriolis forceFz in the Z-axis direction is applied, charges of polarities as shown inFIG. 62 are produced in the previously described sensor of FIG. 57,whereas charges of polarities as shown in FIG. 69 are produced in thesensor of this modification. For this reason, when wirings as shown inFIGS. 70 to 72 are implemented to respective electrode layers, it ispossible to determine Coriolis force components Fx, Fy, Fz as potentialdifferences Vx, Vy, Vz, respectively.

For example, with respect to the operation for detecting Coriolis forceFx in the X-axis direction, since polarities of charges produced atelectrode layers L2, M2 and L4, M4 are inverted, the wiring shown inFIG. 63 is replaced by the wiring shown in FIG. 70. Similarly, withrespect to the operation for detecting Coriolis force Fy in the Y-axisdirection, since polarities of charges produced at electrode layers L6,M6 and L8, M8 are inverted, the wiring shown in FIG. 64 is replaced bythe wiring shown in FIG. 71. In addition, with respect to the operationfor detecting Coriolis force Fz in the Z-axis direction, sincepolarities of charges of electrode layers L10, M10, L11, M11, L14, M14,and L15, M15 are inverted, the wiring shown in FIG. 65 is replaced bythe wiring shown in FIG. 72.

It is to be noted that in the case where the piezoelectric element 540having localized polarization characteristic is used, an a.c. signalapplied in order to oscillate the oscillator 550 is simplified. Namely,in order to oscillate the oscillator 550 in the X-axis direction, it issufficient to deliver a.c. signals in phase to all the localizedelements D1 to D4 as shown in FIG. 68. Similarly, in the case ofoscillating the oscillator 550 in the Y-axis direction, it is sufficientto deliver a.c. signals in phase to all the localized elements D5 to D8.In addition, in the case of oscillating the oscillator 550 in the Z-axisdirection, it is sufficient to deliver a.c. signals in phase to all thelocalized elements D9 to D16.

The wirings shown in FIGS. 70 to 72 have significant merits inmanufacturing actual sensors as compared to the wirings shown in FIGS.63 to 65. The feature of the wirings shown in FIGS. 70 to 72 resides inthat even in the case where a Coriolis force is applied in any directionof the X-axis, the Y-axis and the Z-axis, if Coriolis force is appliedin the positive direction of each axis, positive charges and negativecharges are necessarily produced on the upper electrode layer side andon the lower electrode layer side, respectively. By making use of thisfeature, it is possible to simplify wiring of the entirety of thesensor. Let consider the case where, e.g., terminals Tx2, Ty2, Tz2 inFIGS. 70 to 72 are connected to sensor casing 560 to take a potentialthereon as a reference potential (earth). In this case, sixteen lowerelectrode layers M1 to M16 are in the state where they are conductivewith each other. Even if such an approach is employed, a potentialdifference Vx indicating Coriolis force Fx in the X-axis direction isobtained as a voltage with respect to the earth of terminal Tx1, apotential difference Vy indicating Coriolis force Fy in the Y-axisdirection is obtained as a voltage with respect to the earth of terminalTy1, and a potential difference Vz indicating Coriolis force Fz in theZ-axis direction is obtained as a voltage with respect to the earth ofterminal Tz1. Accordingly, this sensor operates without any hindrance.In addition, since wiring with respect to sixteen lower electrode layersM1 to M16 is carried out by allowing them to be conductive with eachother, the wiring can be very simple.

<5.6> Modification 2

In the case where piezoelectric element 540 having localizedpolarization characteristic is used as in the above-describedmodification 1, it is possible to provide wiring which allows sixteenlower electrode layers M1 to M16 to be conductive. As stated above, iflower electrode layers M1 to M16 are permitted to be conductive, thereis no necessity of allowing these sixteen electrode layers to beintentionally independent electrode layers, respectively. Namely, asshown in the side cross sectional view of FIG. 73, it is sufficient toprovide only one common lower electrode layer M0. The common lowerelectrode layer M0 is a single doughnut disk shaped electrode layer, andserves as an electrode opposite to all the sixteen upper electrodelayers L1 to L16.

<5.7> Modification 3

In order to further simplify the structure of the above-describedmodification 2, it is sufficient to use flexible substrate 570 comprisedof a conductive material (e.g., metal) in place of flexible substrate510. If such flexible substrate 570 is used, the structure in which thelower surface of the piezoelectric element 540 is directly connected tothe upper surface of the flexible substrate 570 can be realized withoutusing special lower electrode layer M0 as shown in the side crosssectional view of FIG. 74. In this case, the flexible substrate 570itself functions as a common lower electrode layer M0.

In addition, while the lower electrode side is caused to be a commonsingle electrode layer in the above-described modifications 2, 3, theupper electrode layer side may be a common single electrode layer in amanner opposite to the above.

<5.8> Other Modifications

While the above-described sensors all use a physically singlepiezoelectric element 520 or 540, they may be constituted withphysically plural piezoelectric elements. For example, in FIG. 59, theremay be employed a configuration in which respective localized elementsD1 to D16 are constituted with separate independent piezoelectricelements thus to use sixteen piezoelectric elements in total. Further,there may be employed a configuration in which one localized elementsare used with respective two localized elements such that a singlelocalized element is used for localized elements D1, D2 and anotherpiezoelectric element is used for localized elements D3, D4, thus to useeight piezoelectric elements in total. As stated above, how manypiezoelectric elements are used from a physical point of view is thematter which can be suitably changed in design.

§6 Sixth Embodiment

<6.1> Principle of Sensor According to Sixth Embodiment

A multi-axial angular velocity sensor according to the sixth embodimentwhich will be described below is a sensor using a electromagnetic forceas the oscillating mechanism and using a differential transformer as thedetecting mechanism. First, its principle will be briefly described withreference to FIG. 75. A center of gravity position of an oscillator 610comprised of a magnetic material is assumed to be origin O to define anXYZ three-dimensional coordinate system. Then, a pair of coils J1, J2, apair of coils J3, J4 and a pair of coils J5, J6 are provided in such amanner that the oscillator 610 is put therebetween.

When six coils are disposed in this way, it is possible to oscillate theoscillator 610 comprised of magnetic material in an arbitrary axis ofthe X-axis, the Y-axis, the Z-axis. For example, in order to produceoscillation Ux in the X-axis direction, it is sufficient to allow acurrent to reciprocally flow in coils J1, J2 arranged on the X-axis.When current is caused to flow in coil J1, the oscillator 610 moves inthe positive direction of the X-axis by magnetic force produced by coilJ1. Further, when current is caused to flow in coil J2, the oscillator610 moves in the negative direction of the X-axis by magnetic forceproduced by coil J2. Accordingly, when current is caused to flowreciprocally, the oscillator 610 is reciprocated in the X-axisdirection. Similarly, in order to produce oscillation Uy in the Y-axisdirection, it is sufficient to allow current to reciprocally flow incoils J3, J4 arranged on the Y-axis. In addition, in order to produceoscillation Uz in the Z-axis direction, it is sufficient to allowcurrent to reciprocally flow in coils J5, J6 arranged on the Z-axis.

On the other hand, by sixth coils arranged in this way, it is alsopossible to detect displacement of the oscillator 610 comprised ofmagnetic material. For example, in the case where the oscillator 610 iscaused to undergo displacement in the positive direction of the X-axis,the distance between the oscillator 610 and coil J1 becomes smaller, andthe distance between the oscillator 610 and coil J2 becomes greater.Generally, when a change takes place in the distance of magneticmaterial with respect to coil, a change takes place in inductance ofthat coil. Accordingly, if inductance change of coil J1 and inductancechange of coil J2 are detected, it is possible to recognize displacementin the X-axis direction of the oscillator 610. Similarly, by inductancechange of coil J3 and inductance change of coil J4, it is possible torecognize displacement in the Y-axis direction of the oscillator 610. Inaddition, by inductance change of coil J5 and inductance change of coilJ6, it is possible to recognize displacement in the Z-axis direction ofthe oscillator 610. In view of this, if there is employed a structuresuch that displacement takes place in the oscillator 610 by Coriolisforce, it is possible to detect Coriolis force components in respectiveaxes directions by inductance changes of respective coils.

While coils J1 to J16 serve as both the role for oscillating theoscillator 610 and the role for detecting displacement of the oscillator610 as stated above, coils for oscillation and coils for detection maybe separately provided.

<6.2> Structure and Operation of Actual Sensor

FIG. 76 is a side cross sectional view showing an actual structure of amulti-axial angular velocity sensor based on the above-describedprinciple. A columnar oscillator 610 comprised of a magnetic materialsuch as iron, etc. is accommodated within a sensor casing 620. Apartition plate 630 is connected on the upper surface of the sensorcasing 620. A disk-shaped diaphragm 640 is attached on the upper surfaceof the partition plate 630 in such a manner that it faces downwardly.The upper end of a connecting rod 650 is fixed to the center of thisdiaphragm. A penetration hole is formed at the central portion of thepartition plate 630. The connecting rod 650 is inserted through thepenetration hole. The oscillator 610 is attached to the lower end of theconnecting rod 650. The oscillator 610 is in a hanging state by theconnecting rod 650 within the sensor casing 620. Further, a protectivecover 660 is attached at the upper part of the partition plate 630 so asto cover the diaphragm 640.

It is now assumed that a center of gravity position of the oscillator610 is taken as the origin, and a Y-axis is taken in a right direction,a Z-axis is taken in an upper direction and an X-axis is taken in adirection perpendicular to plane surface of paper in FIG. 76.

Inside sensor casing 620, six coils J1 to J6 are disposed as shown(although coils J1, J2 are not shown in FIG. 76, coils J1, J2 arerespectively disposed on this side of the oscillator 610 and on thatside thereof). This arrangement is the same as the arrangement shown inFIG. 75.

As described above, a current is caused to flow in a predetermined pairof coils, thereby making it possible to oscillate the oscillator 610 ina predetermined axial direction. Further, inductance change of apredetermined pair of coils is detected, thereby making it possible todetect Coriolis force components exerted in a predetermined axialdirection. Accordingly, it is possible to detect an angular velocityabout a predetermined axis on the basis of the fundamental principleshown in FIGS. 3 to 5.

§7 Detecting Operation

<7.1> Detection of Acceleration

While various embodiments which have been described are all directed tomulti-axial angular sensors, these sensors really have a double functionnot only as a multi-axial angular sensor but also as a multi-axialacceleration sensor. This is indicated in connection with the sensor ofthe first embodiment. FIG. 15 is a view for explaining the operation fordetecting angular velocity ωx about the X-axis. In order to detectangular velocity ωx, it is sufficient to measure Coriolis force Fyexerted in the Y-axis direction in the state where the oscillator 130 iscaused to undergo oscillation Uz in the Z-axis. Meanwhile, the reasonwhy such Coriolis force Fy in the Y-axis direction is produced is thatthe oscillator 130 was caused to intentionally undergo oscillation inthe Z-axis direction in the state where angular velocity ωx is exerted.If the oscillator 130 is not oscillated, Coriolis force Fy is notproduced. However, even if the oscillator 130 is not oscillated, thereare instances where force Fy to move the oscillator 130 in the Y-axisdirection takes place. This is the case where an acceleration in theY-axis direction is applied to the oscillator 130. In accordance withthe fundamental rule of dynamics, when an acceleration is applied to abody having mass, a force proportional to the mass of the body isapplied in the same direction as that of this acceleration. Accordingly,in the case where an acceleration in the Y-axis direction is applied tothe oscillator 130, a force Fy in the Y-axis direction having amagnitude proportional to mass of the oscillator 130 is applied. Suchforce Fy resulting from acceleration and Coriolis force Fy are entirelythe same as force. Accordingly, it is possible to detect a forceresulting from acceleration by exactly the same method as the method ofdetecting Coriolis force.

Eventually, in the above-described sensors of the respectiveembodiments, a force detected in a predetermined axial direction, withan oscillator being intentionally oscillated in a predetermined axialdirection, is Coriolis force. The magnitude of this Coriolis force takesa value corresponding to an angular velocity about a predetermined axis.On the contrary, a force detected in a predetermined axial direction,with an oscillator being not oscillated, is a force based on anacceleration exerted in that axial direction. The magnitude of thisforce takes a value corresponding to the acceleration in the axialdirection. As stated above, when measurement is carried out with anoscillator being oscillated, the above-described sensors of therespective embodiments function as an angular sensor, while whenmeasurement is carried out with an oscillator being not oscillated, theyfunction as an acceleration sensor.

<7.2> Time-divisional Detecting Operation

As described above, the sensors according to this invention serve asboth the function as a multi-axial angular velocity sensor and thefunction as a multi-axial acceleration sensor. In view of this, inpractice, a time-divisional detecting operation as indicated by theflowchart of FIG. 77 is carried out, thereby making it possible to carryout detection of sixth components of acceleration αx in the X-axisdirection, acceleration αy in the Y-axis direction, acceleration αz inthe Z-axis direction, angular velocity ωx about the X-axis, angularvelocity ωy about the Y-axis, and angular velocity ωz about the Z-axis.

First, at step S1, detections of accelerations αx, αy, αz in respectivedirections are carried out at the same time. Namely, it is sufficient tocarry out the detecting processing identical to the detection ofCoriolis force without oscillating oscillator. A force which has beendetected at this time is not Coriolis force in fact, but a forceproduced on the basis of acceleration. With respect to the acceleration,it is possible to detect three axial components at the same time. Thisbecause since there is no necessity of carrying out a work for allowingan oscillator to undergo oscillation, respective electrode layers arenot required to perform the role as the oscillating mechanism, butperforms only the role as the detecting mechanism. For example, in thecase of the sensor according to the fourth embodiment shown in FIG. 42,circuits as shown in FIGS. 46 to 48 are formed for the purpose ofdetecting Coriolis force. In the case of carrying out detection ofacceleration, there is no necessity of delivering an a.c. signal forproducing oscillation. For this reason, it is unnecessary to deliver ana.c. signal to all of electrode layers E1 to E5 and F1 to F5 shown inthese circuits. Accordingly, potential differences Vx, Vy, Vz detectedby these circuits indicate accelerations αx, αy, αz as they are.

Subsequently, detection of angular velocity ωx is carried out at stepS2, detection of angular velocity ωy is carried out at step S3, anddetection of angular velocity ωz is carried out at step S4. With respectto the angular velocity, as previously described, it is unable to detectrespective angular velocity components about three axes. Accordingly,detections of respective angular velocity components are carried out insuccession by such a time division.

Finally, the operation returns from step S5 to step S1 for a secondtime. As long as the detecting operation is continuously executed,similar operation will be repeatedly executed.

<7.3> Detecting Circuit

Subsequently, the fundamental configuration of the detecting circuit forcarrying out a time-divisional detecting operation as previouslydescribed is shown in FIG. 78. In this figure, block 700 corresponds tovarious embodiments of multi-axial angular velocity sensors which havebeen described above. From a viewpoint of function, this block isillustrated in a manner divided into two sections of oscillating section710 and detecting section 720. The oscillating section 710 is a sectionhaving a function to oscillate an oscillator included therein in apredetermined axial direction. When a drive signal is delivered torespective terminals respectively designated at X, Y, Z, an oscillatoris oscillated in the X-, Y- and Z-axial directions. Further, thedetecting section 720 is a section having a function to output adetection signal indicating a displacement of the oscillator included.From respective terminals designated at X, Y, Z in the figure, detectionsignals of displacements with respect to the X-, Y- and Z-axialdirections are respectively outputted. In a practical sensor, there areinstances where one electrode layer serves as both the function on theoscillating section 710 side and the function on the detecting section720 side, and it is therefore difficult to clearly classify respectivesections constituting the sensor into the oscillating section 710 or thedetecting section 720. However, for convenience, this sensor is assumedto be represented by a simple model such as block 700 by functionallygrasping it.

An oscillation generator 711 is a circuit for generating a drive signalwhich is delivered to respective terminals X, Y, Z of the oscillatingsection 710. In a more practical sense, the oscillation generator 711 isa unit for generating, e.g., an a.c. signal. Multiplexer 712 includesswitches SW1, SW2, SW3, and serves to control a drive signal produced inthe oscillating generator 711 delivered to any one of terminals X, Y, Zof the oscillating section 710. On the other hand, a detection signaloutputted from any one of terminals X, Y, Z of the detecting section 720is delivered to a displacement detecting circuit 721 via a multiplexer722. The multiplexer 722 includes switches SW4, SW5, SW6, and serves toselect a detection signal delivered to the displacement detectingcircuit 721. The displacement detecting circuit 721 detects an actualdisplacement quantity on the basis of the detection signal deliveredthereto to deliver it to a detection value output circuit 730. Acontroller 740 controls the operations of multiplexers 712, 722, anddelivers a control signal to the detection value output circuit 730.

The detecting circuit has been constructed as above. It is to be notedthat FIG. 78 is not an actual circuit diagram indicating an actualcurrent path, but is a view showing the outline of the configuration ofthe detecting circuit. Accordingly, a single line shown in the figureindicates a path for a bundle of control signals or detection signals,but does not indicate the current path itself. For example, although asingle control signal line is only illustrated between switch SW1 andthe oscillating section 710, it is necessary to deliver an a.c. signalhaving a predetermined phase to a plurality of electrode layers for thepurpose of oscillating the oscillator in the X-axis direction inpractice. Therefore, a plurality of current paths are required.

When such a detecting circuit is constructed, the detecting operationshown in the flowchart of FIG. 77 will be executed as follows. Theprocessing for detecting accelerations αx, αy, αz is carried out.Namely, the controller 740 delivers, to multiplexers 712, 722, anindication to allow switches SW1, SW2, SW3 to be all turned OFF, and toallow switches SW4, SW5, SW6 to be all turned ON. As a result, no drivesignal is delivered to the oscillating section 710, and, an intentionalexcitation with respect to the oscillator is not carried out.Accordingly, detection signals outputted from respective terminals X, y,Z of the detecting section 720 at this time are not a signal indicatingCoriolis force, but a signal indicating a displacement produced by aforce based on action of acceleration. Since switches SW4, SW5, SW6 areall ON, three signals are all delivered to the displacement detectingcircuit 721, at which displacement quantities in three axial directionsof X, Y, Z are detected. The controller 740 instructs the detectionvalue output circuit 730 to output detected three displacementquantities as values of acceleration. Thus, the displacement quantitiesin the three axial directions detected at the displacement detectingcircuit 721 are outputted as acceleration values αx, αy, αz from thedetection value output circuit 730, respectively.

Subsequently, the controller 740 carries out processing for detectingangular velocity ωx as processing at step S2. Namely, the controller 740delivers, to multiplexers 712, 722, on the basis of the principle shownin FIG. 3, an indication

to allow switch SW1 to be turned OFF,

to allow switch SW2 to be turned OFF,

to allow switch SW3 to be turned ON,

to allow switch SW4 to be turned OFF,

to allow switch SW5 to be turned ON, and

to allow switch SW6 to be turned OFF.

As a result, the oscillating section 710 allows the oscillator toundergo oscillation Uz in the Z-axis direction. The detecting section720 outputs, from terminal Y, a detection signal indicating displacementin the Y-axis direction of the oscillator by action of Coriolis force Fyproduced at this time. The displacement detecting circuit 721 detects adisplacement quantity in the Y-axis direction on the basis of thisdetection signal. The controller 740 instructs the detection valueoutput circuit 730 to output the detected displacement quantity as avalue of angular velocity ωx about the X-axis. Thus, the displacementquantity in the Y-axis direction detected at the displacement detectingcircuit 721 is outputted as angular velocity ωx from the detection valueoutput circuit 730.

Then, the controller 740 carries out processing for detecting angularvelocity ωy as processing at step S3. Namely, the controller 740delivers, to multiplexers 712, 722, on the basis of the principle shownin FIG. 4, an indication

to allow switch SW1 to be turned ON,

to allow switch SW2 to be turned OFF,

to allow switch SW3 to be turned OFF,

to allow switch SW4 to be turned OFF,

to allow switch SW5 to be turned OFF, and

to allow switch SW6 to be turned ON.

As a result, oscillating section 710 allows the oscillator to undergooscillation Ux in the X-axis direction. The detecting section 720outputs a detection signal indicating displacement in the Z-axisdirection of the oscillator by action of Coriolis force Fz produced atthis time from terminal Z. The displacement detecting circuit 721detects displacement quantity in the Z-axis direction on the basis ofthis detection signal. The controller 740 instructs the detection valueoutput circuit 730 to output the detected displacement quantity as avalue of angular velocity ωy about the Y-axis. Thus, the displacementquantity in the Z-axis direction detected at the displacement detectingcircuit 721 is outputted as angular velocity ωy from the detection valueoutput circuit 730.

Further, the controller 740 carries out processing for detecting angularvelocity ωz as processing at step S4. Namely, the controller 740delivers, to multiplexers 712, 722, on the basis of the principle shownin FIG. 5, an indication

to allow switch SW1 to be turned OFF,

to allow switch SW2 to be turned ON,

to allow switch SW3 to be turned OFF,

to allow switch SW4 to be turned ON,

to allow switch SW5 to be turned OFF, and

to allow switch SW6 to be turned OFF.

As a result, the oscillating section 710 allows the oscillator toundergo oscillation Uy in the Y-axis direction. The detecting section720 outputs a detection signal indicating displacement in the X-axisdirection of the oscillator by action of Coriolis force produced at thistime from terminal X. The displacement detecting circuit 721 detectsdisplacement quantity in the X-axis direction on the basis of thisdetection signal. The controller 740 instructs the detection valueoutput circuit 730 to output the detected displacement quantity as avalue of angular velocity about the Z-axis. Thus, the displacementquantity in the X-axis direction detected at the displacement detectingcircuit 721 is outputted as angular velocity ωz from the detection valueoutput circuit 730.

The above-mentioned processing is repeatedly executed via step S5.Accordingly, if such sensor is mounted in a moving body, it becomespossible to continuously detect acceleration components in three axialdirections and angular velocity components about three axial atrespective time points.

<7.4> Other Detecting Principle of Angular Velocity

The foregoing explanation relating to detection of the multi-axialangular velocity was all based on the fundamental principle shown inFIGS. 3 to 5. On the contrary, detection based on the fundamentalprinciple shown in FIGS. 79 to 81 can be made as well. For example, inthe case of detecting angular velocity ωx about the X-axis, inaccordance with the fundamental principle shown in FIG. 3, a Coriolisforce Fy produced in the Y-axis direction when the oscillator is causedto undergo oscillation Uz in the Z-axis direction is detected. Inaccordance with the fundamental principle shown in FIG. 79, it issufficient to detect Coriolis force Fz produced in the Z-axis directionwhen the oscillator is caused to undergo oscillation Uy in the Y-axisdirection. Similarly, in the case of detecting angular velocity ωy aboutthe Y-axis, in accordance with the fundamental principle shown in FIG.4, Coriolis force Fz produced in the Z-axis direction when theoscillator is caused to undergo oscillation Ux in the X-axis directionis detected. In accordance with the fundamental principle shown in FIG.80, it is sufficient to detect Coriolis force Fx produced in the X-axisdirection when the oscillator is caused to undergo oscillation Uz in theZ-axis direction. In addition, in the case of detecting angular velocityωz about the Z-axis, in accordance with the fundamental principle shownin FIG. 5, Coriolis force Fx produced in the X-axis direction when theoscillator is caused to undergo oscillation Uy in the Y-axis directionis detected. In accordance with the fundamental principle shown in FIG.81, it is sufficient to detect Coriolis force Fy produced in the Y-axisdirection when the oscillator is caused to undergo oscillation Ux in theX-axis direction.

In short, the multi-axial velocity sensor according to this inventionutilizes the natural law that, with respect to an oscillator positionedat the origin of three axes perpendicular to each other, in the casewhere angular velocity ω is applied about the first axis, whenoscillation U is given in the second axial direction, Coriolis force isapplied in the third axial direction. Either selection of principles asshown in FIGS. 3 to 5 or selection of principles as shown in FIGS. 79 to81 may be made. Accordingly, it is possible to carry out detection towhich the fundamental principle shown in FIGS. 79 to 81 is applied inconnection with all the embodiment which have been described above.

<7.5> Detection by Combination of the Fundamental Principles

As described above, in the angular velocity detection according to thisinvention, it is possible to carry out both detection based on thefundamental principle shown in FIGS. 3 to 5 and detection based on thefundamental principle shown in FIGS. 79 to 81, and it is furtherpossible to carry out detection in which both detections are combined.For the purpose of facilitating understanding, classification ofrespective fundamental principles is carried out. It is seen that sixkinds of detecting operations as shown in the following Table can bemade.

TABLE PRINCIPLE <U> <F> <ω> DIAGRAM DETECTING X Y Z FIG. 81 OPERATION 1DETECTING X Z Y FIG. 4 OPERATION 2 DETECTING Y Z X FIG. 79 OPERATION 3DETECTING Y X Z FIG. 5 OPERATION 4 DETECTING Z X Y FIG. 80 OPERATION 5DETECTING Z Y X FIG. 3 OPERATION 6In the above Table, the column of U indicates the axial direction toexcite the oscillator, the column of F indicates the axial direction todetect Coriolis force exerted on the oscillator, and the column of ωindicates the axis relating to angular velocity to be detected. In thedetection based on the fundamental principle shown in FIGS. 3 to 5, eventhree detecting operations of the above Table are carried out. In thedetection based on the fundamental principle shown in FIGS. 79 to 81,odd three detecting operations are carried out. As previously described,it is possible to detect angular velocity components about three axes ofXYZ by such three detecting operations.

Meanwhile, combination for detecting such angular velocity componentsabout three axes is not limited to combination of even and odd detectingoperations. For example, even if combination of the detecting operations1 to 3 of the first half is employed, angular velocity components aboutthree axes of X, Y, Z can be detected. Further, even if combination ofthe detecting operations 4 to 6 of the latter half is employed, angularvelocity components about three axes of X, Y, Z can be made (see thecolumn of ω of the above Table). In addition, when such combinations areemployed, a portion of the oscillating mechanism and the detectingmechanism may be omitted. For example, in order to execute the detectingoperations 1 to 3 in the above Table, it is sufficient for theexcitation axis of the oscillator to employ the X-axis and the Y-axis(see the column of U). In other words, it is not necessary to oscillatethe oscillator in the Z-axis. Further, it is sufficient for the axis fordetecting Coriolis force to employ only the Y-axis and the Z-axis (seethe column of F). In other words, it is not necessary to detect Coriolisforce in the X-axis direction. Eventually, as the oscillating mechanism,it is enough to permit the oscillator to undergo oscillation in two axesdirections of X-axis and the Y-axis. As the detecting mechanism, it isenough to permit detection in two axes of the Y-axis and the Z-axis. Itwas the premise that various embodiments which have been described aboveall include an oscillating mechanism for oscillating an oscillator inthree axial directions of X, Y, Z and a detecting mechanism fordetecting Coriolis force components in three axial directions of X, Y,Z. However, by suitably combining the fundamental principles in thisway, detection of angular velocity components about three axes can bemade by using an oscillating mechanism in two axes directions and adetection mechanism in two axes directions.

While the above-described embodiments were all directed to athree-dimensional angular velocity sensor for detecting angular velocitycomponents about three axes of X, Y, Z, in the case where it issufficient to detect only angular velocity components with respect tospecific two axes of these three axes, it is possible to use atwo-dimensional angular velocity sensor in which a portion of theoscillating mechanism or the detecting mechanism is further omitted. Forexample, let now consider only the detecting operation 1 and thedetecting operation 2 in the above Table. In order to carry out thesetwo detecting operations, it is sufficient that an oscillating mechanismin the X-axis direction and a detecting mechanisms in the Y-axis andZ-axis directions are provided. As a result, it is possible to detectangular velocity about the Z-axis and angular velocity about the Y-axis.Accordingly, a two-dimensional angular velocity sensor can be realizedby the oscillating mechanism in one axial direction and the detectingmechanism with respect to two axes.

In addition, combination as described below may be employed. Let nowconsider only the detecting operation 2 and the detecting operation 3 inthe above Table. In order to carry out these two detecting operations,it is sufficient that an oscillating mechanisms in the X-axis and Y-axisdirections and a detecting mechanism with respect to the Z-axisdirection are provided. As a result, angular velocity about the Y-axisand angular velocity about the X-axis can be detected. Accordingly, atwo-dimensional angular velocity sensor can be realized by theoscillating mechanisms in two axes directions and the detectingmechanism with respect to one axis.

INDUSTRIAL APPLICABILITY

A multi-axial angular velocity sensor according to this invention canrespectively independently detect angular velocity ωx about the X-axis,angular velocity ωy about the Y-axis, and angular velocity ωz about theZ-axis with respect to an object moving in an XYZ three-dimensionalcoordinate system. Accordingly, when mounted in an industrial machine,an industrial robot, an automotive vehicle, an air-plane, or a ship,etc., this multi-axial angular velocity sensor can be widely utilized asa sensor in carrying out recognition of moving state or a feedbackcontrol with respect to movement. In addition, this multi-axial angularvelocity sensor can be also utilized for control to correctunintentional hand movement at the time of photographing by camera.

1. An angular velocity sensor for detecting an angular velocitycomponent comprising: an oscillator made of a substrate with thicknessenough to obtain a mass sufficient to provide the sensor with a requiredsensitivity; a sensor casing for accommodating the oscillatortherewithin; a flexible member for connecting the oscillator to thesensor casing so that the oscillator can be moved with respect to thesensor casing; an electrical driving device for oscillating theoscillator using electrical energy, the electrical driving deviceincluding a first electrode provided on a surface of the oscillator, asecond electrode provided on a surface of a fixed member fixed to thesensor casing and an excitation element applying a voltage between thefirst electrode and the second electrode; and a capacitance elementincluding a pair of electrodes, a distance between the pair ofelectrodes being changed based on a deviation of the oscillator causedby Coriolis force.
 2. An angular velocity sensor according to claim 1,wherein the oscillator is made of a silicon substrate.